Answer:
4
Step-by-step explanation:
f⁻¹(x) = x²+3, but none of that matters, since f(f⁻¹(x)) = x
For this problem you have to isolate the variable. To do this you must inverse the operations. Multiply 18 by 5, then divide by 12 to get your answer of 7.5
So... let's say the amounts invested were "a" at 6% and "b" at 7.5%.
ok.. hmm what's 6% of a? well, (6/100) * a or 0.06a.
what's 7.5% of b? well, (7.5/100) * b or 0.075b.
now... we know, whatever "a" and "b" are, they total the investment of 5000 bucks, thus
a + b = 5000and the interest yielded was 337.50, thus
0.06a + 0.075b = 337.50thus

solve for "a", to see how much was invested at 6%.
what about "b"? well, b = 5000 - a.