Solve each equality and express your answer in the form variable$=$___

1. Solving $\frac{9}{15} a = \frac{4}{17}$ gives the solution

2. Solving $\frac{8}{16} c = \frac{-8}{15}$ gives the solution

3. Solving $\frac{5}{-14} b = \frac{5}{17}$ gives the solution

4. Solving $\frac{-8}{-15} d = \frac{-4}{18}$ gives the solution

Hint: