Please answer the given financial question based on the context.
Context: ||Years ended December 31,||||
||2019|2018|$ Difference |% Difference|
|Selling, general and administrative expense|$24,371,349|$14,794,205|$9,577,144|64.7%|
|Research, development and engineering expense|7,496,012|3,766,160|3,729,852|99.0%|
|Total operating expense|$31,867,361|$18,560,365|$13,306,996|71.7%|
Operating Expense
Selling, general and administrative expense increased $9.6 million to $24.4 million for the year ended December 31, 2019 compared to $14.8 million for the year ended December 31, 2018. Selling, general and administrative expense increased primarily due to $4.4 million of expenses associated with the legacy business of MOI and $2.0 million of expenses associated with the legacy business of GP , in addition to $1.0 million in transaction costs associated with the acquisition of GP, a $0.9 million increase in share-based compensation as a result of new awards, and a $1.1 million increase in expenses related to sales and marketing as a result of increased revenue.
Research, development and engineering expenses increased $3.7 million to $7.5 million for the year ended December 31, 2019 compared to $3.8 million for the year ended December 31, 2018 primarily due to $1.1 million of research, development and engineering expense associated with the legacy business of MOI and $2.7 million of research, development and engineering expense associated with the legacy business of GP during the year ended December 31, 2019.
Question: What is the average Research, development and engineering expense for December 31, 2018 and 2019?
Answer:
5631086