Answer:
(rectangular prism); opposite sides are equal
Area of bottom base;
3 feet x 3 feet = 9 feet,
Area of above base, (9 x 2) = 18
Area of front;
6 feet x 3 feet = 18 feet
Area of back, (18 x 2) = 36
Area of right side;
6 feet x 3 feet = 18 feet
Area of left side, (18 x 2) = 36
Find the sum of all the areas added;
18 + 36 + 36 = 90 square feet