Answer:
48 square units
Explanation:
area of triangle = base * height / 2
base = x+1
height = 8x
area = (x+1)(8x)/2 = (8x²+8x)/2 = 4x²+4x
area of rectangle = length * width = (5x+1)(x) = 5x²+x
set the two areas to be equal to each other
5x²+x = 4x²+4x
divide both sides by x as that is a multiple of each value on each side
5x + 1 = 4x + 4
subtract 4x from both sides to limit the variable to one side
x + 1 = 4
subtract both sides by 1 to isolate the variable
x = 3
area = (5x+1)(x) = (5*3+1)(3) = 16 * 3 = 48 square units