To answer this question you will need to use the information about the circumference to find the area.
Solve for the diameter using the circumference formula.
C = pi x d
157 = 3.14 x d
d = 50 feet
Now use the diameter to find the radius (50/2) of 25 feet.
You can now find the area of the stage.
A = pi x r^2
3.14 x 25^2
A = 1962.5 square feet
To find out how many hours it will take to paint divide the tots area by the number of square feet she can paint per hour.
1962.5/400 = 4.9
Katie will take approximately 5 hours to paint the stage.