Idon't understand how to solve this

Ok so the radius is half the diameter, and the diameter is half the circle.  And the area is the space inside a circle.  And pie is 3.14. 
So if your radius is 10 then you will multiply 10 x 10 to get 100.  Then multiply 100 x pie or 3.14 which you will get, 314cm².  So your answer is 314cm²

The formula for an area of a circle is radius x radius = ? 
Then multiply pie, 3.14 by your new radius x radius, and you got your answer.

The answer is 1 because you have to flip the sign when dividing by negative number and 3