step 1
Find the area of each rectangle
Remember that the area of the rectangle is equal to
A=b*h
First rectangle
A=x*x=x^2 unit2
Second rectangle
A-=12*x=12x unit2
Third rectangle
A=2x*x=2x^2 unit2
step 2
Adds the areas
x^2+12x+2x^2
combine like terms
3x^2+12x