Explanation:
the area of a trapezoid is
(a + b)/2 × x
a and b being the 2 bases. and x, as requested, is the height.
A
it does not matter which base is which, as long as we keep using them consistently.
so, let's assume a is the first base :
a = x + 5
and then for the second base
b = 2x - 1
now we use that in the main formula :
(x + 5 + 2x - 1)/2 × x = (3x + 4)/2 × x = (3x² + 4x)/2
A = (3/2)x² + (4/2)x = (3/2)x² + 2x ft²
B
now the height is increased by 4 ft.
that means we need to replace x by x + 4.
(3/2)(x+4)² + 2(x+4) = (3/2)(x² + 8x + 16) + 2x + 8 =
= (3/2)x² + (24/2)x + (48/2) + 2x + 8 =
= (3/2)x² + 12x + 24 + 2x + 8 =
= (3/2)x² + 14x + 32 ft²
with x being the original height, of course.