AMC 12 2018b Problem 1

Kate bakes a $20$-inch by $18$-inch pan of cornbread. The cornbread is cut into pieces that measure $2$ inches by $2$ inches. How many pieces of cornbread does the pan contain?

$\textbf{(A) } 90 \textbf{(B) } 100 \textbf{(C) } 180 \textbf{(D) } 200 \textbf{(E) } 360$