Help with one math word problem please write directions in words step by step....

Find the unknown base of the trapezoid
A=180FT,B1=?,B2=26FT,H=9FT
please write in words what to do step by step.

I'm going to assume the following given that this isn't all too clear:

A = Area = 180
B1 = one parallel side of the trapezoid
B2 = the other parallel side
H = height of the trapezoid

Area of a trapezoid = average of the two parallel sides multiplied by the height
Averaging the parallel sides effectively is the same as shortening the long one and lengthening the short one until you get a rectangle and then area of a rectangle is width multiplied by height. Hope that makes sense? so this progresses:

Area of a trapezoid = average of the two parallel sides multiplied by the height
Area = Average x Height
Area = (B1 + B2)/2 x Height
180 = (B1 + B2)/ 2 x 9

Let's get rid of the horrible "divide by two"

180 x 2 = (B1 + B2) x 9
360 = (B1 + B2) x 9

dividing by 9:

360 / 9 = B1 + B2
40 = B1 + B2

we were given B2 as 26

40 = B1 + 26
40 - 26 = B1
14 = B1