#### Answer

7, $\frac{5}{3}$

#### Work Step by Step

a. We are given the equation $4=\frac{m}{7}$. In order to solve, we need to multiply both sides by 7, which will simplify the right side to $\frac{m}{7}\times7=m$. Doing so will allow us to isolate the variable on one side.
b. We are given the equation $-15=\frac{3}{5}r$. In order to solve, we need to multiply both sides by $\frac{5}{3}$, which will simplify the right side to $\frac{3}{5}r\times\frac{5}{3}=r$. Doing so will allow us to isolate the variable on one side.