Variant 9.2.1. On the sides $AB$ and $AD$ of rectangle $ABCD$, points $M$ and $N$ are marked, respectively. It is known that $AN=7$, $NC=39$, $AM=12$, $MB=3$.

(a) (1 point) Find the area of rectangle $ABCD$.

(b) (3 points) Find the area of triangle $MNC$.

![](https://cdn.mathpix.com/cropped/2024_05_06_1f4981519479532effc1g-09.jpg?height=423&width=603&top_left_y=717&top_left_x=421)
Answer: (a) 645. (b) 268.5.