Area of circle=pi x radius ^2, if the line through the center of the circle goes from one end to the other, it is the diameter, so you need to divide it by 2 before you put it into the formula. If the line is only half way, then it is already the radius, so use that number in the formula.
2. the line is half way only, so it is the radius=21. You can use it in the formula:
a=3.14 x 21 ^2
a=3.14x441
a =1384.74
3. the line goes all the way to the other side of the circle, so it is the diameter=56. you need to divide it by 2 to get the radius: so 56/2=28=radius. Now us 28 in the formula:
3.14 x 28^2
a=3.14 x 784
a=2461.76.
just continue doing that for the rest of the problems. Hope this helps.