CAYLEY 2021 Problem 25

The points J(2,7), K(5,3) and L(r, t) form a triangle whose area is less than or equal to 10 . Let \mathcal{R} be the region formed by all such points L with 0 \leq r \leq 10 and 0 \leq t \leq 10. When written as a fraction in lowest terms, the area of \mathcal{R} is equal to \frac{300+a}{40-b} for some positive integers a and b. The value of a+b is

Answer Choices
A. 82
B. 71
C. 60
D. 49
E. 93