Please answer the given financial question based on the context.
Context: |($ in millions)||||
|For the year ended December 31:|2019|2018|2017|
|Cost|$100|$82|$91|
|Selling, general and administrative|453|361|384|
|Research, development and engineering|126|67|59|
|Pre-tax stock-based compensation cost|679|510|534|
|Income tax benefits|(155)|(116)|(131)|
|Net stock-based compensation cost|$524|$393|$403|
The following table presents total stock-based compensation cost included in income from continuing operations.
Total unrecognized compensation cost related to non-vested awards at December 31, 2019 was $1.2 billion and is expected to be recognized over a weighted-average period of approximately 2.5 years.
Capitalized stock-based compensation cost was not material at December 31, 2019, 2018 and 2017.
Question: What was the increase / (decrease) in the cost from 2018 to 2019?
Answer:
18