Question 255604
Since the perimeter is 100 the sides are 25 each.
The diagonals are perpendicular and meet in the center of the circle.
There is a right triangle with a side of 40/2=20 and hypotenuse of 25. 
20^2+b^2=25^2
400+b^2=625
b^2=225
b=15
(15*20)/2=150 sq cm Area of triangle.
Draw a line from the right angle, which is also the center of the circle, perpendicular to the hypotenuse and label it x.
25x/2=150
25x=300
x=12 radius of the circle.
pi*12^2=144pi sq cm area of the circle.
.
Ed