What is value of $b$ in the following system of equations ? <BR> $\qquad 4a = 28$ <BR> $\qquad 15-2a = 5b$

Question

$\begin{array}{1 1} (a)\;5 \\ (b) \; \frac{1}{5} \\ (c)\;-5 \\ (d)\;-\frac{1}{5} \end{array}$