(3) (4 pts) Suppose $a$ and $b$ are integers, $3 \equiv a(\bmod 19)$, and, $11 \equiv b(\bmod 19)$. Find the integer $c$ with $0 \leq c \leq 18$ such that $c \equiv a-b(\bmod 19) $ (4) (4 pts) Let $a, b, c, d$, and $m$ be integers where $$ is a positive integer. Show that if $a \equiv b(\bmod m)$ and $c \equiv d\bmod m)$, then $a c \equiv b d\bmod m)$. CS.PB.004