Answer: 1,000
First, you have to find how much 7.5% is coming out of 10,000. So in this case it's 750. Multiply 750 by 12 years. Thats 9000, you then subtract 9000 and 10,000 to get 1,000.
F(x) = 112 - kx
f(-3) = 121
f(-3) = 112 - k(-3)
f(-3) = 112 + 3k
121 = 112 + 3k
121 - 112 = 3k
9 = 3k
9/3 = k
3 = k <===
Well you do 228/12 to find your answer and that is 19 and to check you do 12*19=228