Read the following texts and table with financial data from an S&P 500 earnings report carefully.Based on the question-answer history (if provided), answer the last question. The answer may require mathematical calculation based on the data provided.

Text: marathon oil corporation notes to consolidated financial statements stock-based performance unit awards 2013 during 2018 , 2017 and 2016 we granted 754140 , 563631 and 1205517 stock- based performance unit awards to officers . at december 31 , 2018 , there were 1196176 units outstanding . total stock-based performance unit awards expense was $ 13 million in 2018 , $ 8 million in 2017 and $ 6 million in 2016 . the key assumptions used in the monte carlo simulation to determine the fair value of stock-based performance units granted in 2018 , 2017 and 2016 were: . <table class='wikitable'><tr><td>1</td><td>-</td><td>2018</td><td>2017</td><td>2016</td></tr><tr><td>2</td><td>valuation date stock price</td><td>$ 14.17</td><td>$ 14.17</td><td>$ 14.17</td></tr><tr><td>3</td><td>expected annual dividend yield</td><td>1.4% ( 1.4 % )</td><td>1.4% ( 1.4 % )</td><td>1.4% ( 1.4 % )</td></tr><tr><td>4</td><td>expected volatility</td><td>39% ( 39 % )</td><td>43% ( 43 % )</td><td>52% ( 52 % )</td></tr><tr><td>5</td><td>risk-free interest rate</td><td>2.5% ( 2.5 % )</td><td>2.6% ( 2.6 % )</td><td>2.4% ( 2.4 % )</td></tr><tr><td>6</td><td>fair value of stock-based performance units outstanding</td><td>$ 19.60</td><td>$ 19.45</td><td>$ 21.51</td></tr></table> 18 . defined benefit postretirement plans and defined contribution plan we have noncontributory defined benefit pension plans covering substantially all domestic employees , as well as u.k . employees who were hired before april 2010 . certain employees located in e.g. , who are u.s . or u.k . based , also participate in these plans . benefits under these plans are based on plan provisions specific to each plan . for the u.k . pension plan , the principal employer and plan trustees reached a decision to close the plan to future benefit accruals effective december 31 , 2015 . we also have defined benefit plans for other postretirement benefits covering our u.s . employees . health care benefits are provided up to age 65 through comprehensive hospital , surgical and major medical benefit provisions subject to various cost- sharing features . post-age 65 health care benefits are provided to certain u.s . employees on a defined contribution basis . life insurance benefits are provided to certain retiree beneficiaries . these other postretirement benefits are not funded in advance . employees hired after 2016 are not eligible for any postretirement health care or life insurance benefits. .
Question: what was the total stock-based performance unit awards expense in the years of 2017 and 2018, in millions?
Answer: 21.0
Question: including the year of 2016, what would then be the total in stock-based performance unit awards expense of the three years, in millions?

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27.0
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