GMAT Quantitative Reasoning Practice Test 3

The easiest way is to back solve the question.
Take answer $\mathrm{\$}120,000$, if that is the amount Jennifer invested in the second apartment; the annual return from that apartment was $\left(120,000\mathrm{times}0.24=28,800\right)$.Therefore, there are $\mathrm{\$}180,000$ left to invest in the first apartment, $18\%$ of $\mathrm{\$}180,000$ is $\mathrm{\$}32,400$.
Sum them up; the total return is like the question asked $-\mathrm{\$}61,200$.