So remember that the area of a trapezoid is
, with b = bases and h = height. Before we can do the equation, however, we have to find the height. Using the right triangle, we can use the pythagorean theorem, which is
.
Since we know that the hypotenuse is 13 and one of the legs is 12, we can solve for the other leg. Our equation will look like this: 
Firstly, solve the exponents: 
Next, subtract 144 on both sides: 
Next, square root both sides, and your height will be: x = 5
Now that we know both the height, 5, and the bases, 30 and 40, we can solve for the area of the trapezoid. Our equation will look like this: 
Firstly, combine everything on the numerator: 
Next, divide the fraction: 
Next, multiply, and your answer will be A = 175 un^2.