Final answer:
The amount of construction costs incurred during 2015 is $2,000,000
Step-by-step explanation:
The construction costs incurred during 2015 can be calculated by finding the difference in the estimated total cost of the contract between December 31, 2014 and December 31, 2015. In 2014, the estimated total cost was $18,000,000, and in 2015, it was $20,000,000. Therefore, the difference in cost is $20,000,000 - $18,000,000 = $2,000,000.