1. area of semi circle?

hi i need to find the area of this:

im not sure how to do it because there isn't a radius there. if anyone can help and explain i will be very thankful!

2. is 26 the diameter of the semicircle so i half it to make the radius so i would do, pie x 13 x13 to make the area of a circle then divide by 2 to make area of a semicircle?