This is a multistep problem. So, let's split it up.
Finding the height: We need to look at the equation for find the diagonal of a triangle. a²+b²=c² We don't have leg one, but we have leg two. If we subtract the longer base by the shorter base, we have leg two. 11-7=4 a²+4²=5² a²+16=25; let's subtract 16 from both sides. a²=9 a=3
So, the height is 3.
Finding the area of the trapzoid: Let's look at the formula for finding the area. (b1+b2)(h÷2)=A; let's fill the variables in. (7+11)(3÷2)=A (18)(1.5)=A 27=A