we know that
volume of triangular prism=area of the base*height
step 1
find the area of the base
area of triangle=b*h/2
is a right triangle
b=18 in----> convert to ft-----> 18*0.0833----> 1.50 ft
h=2 ft
area of triangle=1.5*2/2----> 1.5 ft²
volume of triangular prism=1.5*3----> 4.5 ft³
the answer is 4.5 ft³