it is given that,
the height of the wedge is h = 18 in
the area of the wedge is A = 90 square in.
we know that the area of a triangle is
A = 1/2 x base x height
put values,
90 = 1/2 x base x 18
90/18 = 1/2 x base
5 = 1/2 x base
base = 5 x 2
base = 10 inches,
thus, the base of the wedge is 10 inches,