Chapter 1 - Section 1.7 - Problem Solving: Interest, Mixture, Uniform Motion, Constant Rate Job Applications - 1.7 Asses Your Understanding - Page 141: 20

See below.

Let $x$ be the amount she invests in B-rated bonds and then $50000-x$ is the amount invested in CDs, then our equation is: $1.15x+(50000-x)1.07=57000\\1.15x+53500-1.07x=57000\\0.08x=3500\\x=43750$ So $43750$ should be the amount she invests in B-rated bonds and then $6250$ is the amount invested in CDs