How do you solve this

I would use the little formula in the upper left corner. In fact, I betcha that's WHY it's there. It's the formula for any amount growing with interest compounded annually. ... The 'B' is the principle ... that's your 1,100. The 'I' is the interest factor. For 8%, I is 1.08. And the little 'n' exponent is the number of years it grows. When you're done, the total result is what it's worth after 15 years. When you subtract off the original 1,100 the rest is the interest it earned.