Martina invested her savings in two investment funds. the $12,000 that she invested in fund a returned a 5% profit. the amount that she invested in fund b returned a 1% profit. how much did she invest in fund b, if both funds together returned a 4% profit?

we know she invested 12000 in A, and say "b" dollars in B, so the total amount invested or principal must be 12000 + b.

we also know that those profits added together, yielded only 4% of the total amount invested, namely 4% of (12000 + b), which will be 0.04(12000 + b).

they would have to work 32 hours.