Area of a triangle = 1/2 x base x height
Area of original triangle = 1/2 x 7 x 10 = 35 square feet.
Add 1.5 feet to area to get 35 + 10.5 = 45.5 square feet.
Solve for the new height:
45.5 = 1/2 x 7 x H
Multiply both sides by 2:
91 = 7 x H
Divide both sides by 7:
H = 91/7
H = 13 feet
The new height needs to be 13 feet.
13 - 10 = 3 feet
The height has to increase by 3 feet.