**Answer:**

The correct option is **a. 2017: $200,000 2018: $520,000 2019: $240,000**.

**Explanation:**

The formula for cost to cost method is expected or actual cost incurred to date divided by the total cost of the project or contract.

Therefore, we have:

Total cost = Cost in 2017 + Cost in 2018 + Cost in 2019 = $640,000 + $1,600,000 + $800,000 = $3,040,000

Cost in 2017 contribution to total cost = Cost in 2017 / Total cost = $640,000 / $3,040,000 = 0.21

Cost in 2018 contribution to total cost = Cost in 2018 / Total cost = $1,600,000 / $3,040,000 = 0.53

Cost in 2019 contribution to total cost = Cost in 2019 / Total cost = $800,000 / $3,040,000 = 0.26

Revenue in 2017 = Cost in 2017 contribution to total cost * Contract price = 0.21 * $4,000,000 = $840,000

Revenue in 2018 = Cost in 2018 contribution to total cost * Contract price = 0.53 * $4,000,000 = $2,120,000

Revenue in 2019 = Cost in 2019 contribution to total cost * Contract price = 0.26 * $4,000,000 = $1,040,000

Therefore, **net income for each year 2017 through 2019 using the cost-to-cost method can be computed as follows**:

Net income for year 2017 = Revenue in 2017 - Cost in 2017 = $840,000 - $640,000 = $200,000

Net income for year 2018 = Revenue in 2018 - Cost in 2018 = $2,120,000 - $1,600,000 = $520,000

Net income for year 2019 = Revenue in 2019 - Cost in 2019 = $1,040,000 - $800,000 = $240,000

Therefore, the correct option is **a. 2017: $200,000 2018: $520,000 2019: $240,000**.