For this, you can use the formula for the area of a circle. The formula is pi*radius*radius
Look at this figure as 1/4 of a circle. You can do this because the measure of the angle of the corner is 90 degrees, and 90 is 1/4 of 360.
Since the radius of the full circle would be 10, the area would be pi*10*10=100pi
Since this figure is 1/4 of that, the area is 25pi.
Hope this helps!
