Suppose that a point (X, Y) is chosen at random from the region S in the xy-plane

Question:

Suppose that a point (X, Y) is chosen at random from the region S in the xy-plane containing all points (x, y) such that x ≥ 0, y ≥ 0, and 4y + x ≤ 4.
a. Determine the joint p.d.f. of X and Y.
b. Suppose that S0 is a subset of the region S having area α and determine Pr[(X, Y ) ∈ S0].