This is 6th-grade math just find the area of the triangle-
A= 1/2 (b) (h)

Answer:
Formula for area:
[tex]area = \frac{1}{2} \times( base) \times (height) \\ \\ { \boxed{A = \frac{1}{2}(b)(h) }}[/tex]
according to triangle given;
base, b » 30 ft
height, h » 40 ft
substitute the variables for the equation:
[tex]A = \frac{1}{2} \times (30) \times (40) \\ \\ A = 30 \times 20 \\ \\ { \boxed{ \boxed{area \: \: A = 600 \: {ft}^{2} }}}[/tex]