Let b=base length. Area=bh where h=height=b/2+2 so area=b(b/2+2)=b^2/2+2b.
So what is 10 inches? We have to find base and area. Assume b=10" initially, then h=7" and area = 70 sq in.
OK. Now assume slant side length is 10". We have insufficient information because we don't have the angle of slope.
Therefore, we have to go with the initial assumption that the base has a given length of 10" and h=(10/2+2)=7" so the area is 70 sq in.