The formula for calculating the area of a trapezoid is given by;
[tex]A=\frac{a+b}{2}h[/tex]where a and b are the base and h is the height
From the question,
a = 5
b= 13
h = 3
substitute the vakues into the formula
[tex]A=\frac{5+13}{2}(3)[/tex][tex]A=\text{ 9}\times3[/tex][tex]A=27ft^2[/tex]