Answer: 26 square feet (choice D)
Work Shown:
base = 13 = horizontal component
height = 4 = vertical component
The base and height are always perpendicular, meaning they meet at right angles.
area of triangle = base*height/2
area of triangle = 13*4/2
area of triangle = 52/2
area of triangle = 26 square feet
the notation ft^2 means "square feet"