On a road, a bike sign in the shape of an isosceles trapezoid is to be painted. The sign and its dimensions are shown below. What is the area of the sign?
A right trapezoid is shown with a height labeled 4 feet and one of the bases labeled as 9 feet, and the other base is labeled as 7 feet.
A. 24 square feet
B. 28 square feet
C. 30 square feet
D. 32 square feet