If $130\% $ of $a$ is equal to $70\%$ of $b$, which of the following is equal to $a-b$?

Question

$\begin{array}{1 1} (a)\; \dfrac{6}{13}b \\ (b)\; \dfrac{-6}{3}b \\ (c)\; \dfrac{13}{6}b \\ (d)\; \dfrac{-13}{6}b \end{array}$