So,
1st year: 3
2nd year: 4(first year), which is 12
3rd year: 6(first year), which is 18
The sum of the 1st, 2nd, and 3rd years is 3 + 12 + 18 = 33
Now, multiply 33 by the price at which Mr. Jackson sold each computer ($185).
We get $6105. Mr. Jackson's gross profit was $6105.