I'm going to assume the rate, 3.9%, is for one year.
7550 * 3.9 * 6 = $176, 670 is the simple interest earned in 6 years with a rate of 3.9% per year.
Since you have the formula, why don't you do it yourself?
2(x+7) + x=20
(2)(x) + (2)(7) + x=20 Distribute
2x+14 + x =20
(2x+x) + (14) =20 Combine Like Terms
3x+14=20
- 14 -14 Subtract 14 from both sides
3x = 6
3x/3 6/3 Divide Both Sides by 3
x = 2
Let me know if you still don't understand
wow the answer is not listed on option