There is another point of intersection at (0,0). Let's call the functions x1 and x2 with x2 always being greater for the interval. Therefore the area is
Integral from 0 to 5/2 of (x2 - x1) dy (adding up horizontal rectangles in y)
integral from 0 to 5/2 of (y-y2-y2+4y)dy = 5y2/2 - 2y3/3 evaluated from 0 to 5/2
(5/2)3 - (2/3)(5/2)3 = (1/3)(5/2)3 = 125/24
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