To find the area, you first must find the hypotenuse of the top triangle.
a^2 + b^2 = c^2
18^2 + 24^2 = c^2
18 and 24 are both divisible by 6, so you can divide them both by 6 to make the equation easier to solve.
3^2 + 4^2 = c^2
25 = c^2, so c = 5
Multiply 5 by the 6 we divided by earlier to get a hypotenuse of 30.
The area equals base times height divided by two, so we can divide 84 by 2 and then multiply by 30 to get the area.
84/2= 42
42 x 30 = 1260 inches squared is the area