Probably an easier way, but.....
Height of triangle EAD =10
(1/2) the base = 5
Slope of line through AE = 10/5 = 2
So....Let the line through AE have the equation y =2(x - 10) = 2x -20
Slope of line through CD = [ 10 -0 ] / [0 -20 ] = -1/2
So....Let the line through CD have the equation y = (-1/2)x + 10
Find the intersection of these lines = x coordinate of N
2x -20 = (-1/2)x + 10
(5/2)x = 30
x = 12
The y coordinate of A is y = (-1/2)(10) + 10 = 5 = base of triangle formed by shaded region
(12 -10) = 2 = height of triangle formed by the shaded region
Shaded region = (1/2) (5) * 2 = 5