$y=mx+c$, where $m$ and $c$ are constants. When $x=5$ => $y=25$. When $x=10$ => $y=35$. What is the value of $c$ ?

Question

$\begin{array}{1 1} (a)\;16 \\ (b)\;25 \\ (c)\;18 \\(d)\;19 \end{array}$