Area/Sector of a circle: A cow is tethered by a 100-ft rope to the inside corner of an L-shaped building A cow is tethered by a $100ft$ rope to the inside corner of an L-shaped building, as shown in the figure. Find the area that the cow can graze. (Let 
$a = 30 ft$, $b = 60 ft$, $c = 100 ft$, $d = 70 ft$, and $e = 60 ft$.
 Round your answer to the nearest whole number.)
If anyone could explain to me what to do to solve this that would be great! I think just explaining what the first step or two should be will be enough for me to understand the rest on my own (like a hint).

EDIT: 
Did I make a mistake here?
$\frac{1}{4}*\pi*(40)^2$, 
$\frac{1}{4}*\pi*(40)^2$, 
$\frac{1}{4}*\pi*(10)^2$, 
$\frac{1}{4}*\pi*(100)^2$
 A: There are four quarter circles of radius accessible for grazing for each area centered on a wall corner as you sketched. 
$$ c,\, c-b,\, c-b-a , \,c-d. $$
A: Hint: the area in the picture is divided into different quarters of circles; find the radius of each, use that to find each area, and then add them up.
For example, the radius of the quarter-circle on the bottom right is $c-d=30$ ft, so its area is $\frac 14 \pi r^2=\frac 14 \pi (30)^2= {900\pi \over 4}$ft$^2$

EDIT: The radii, from the bottom right anti-clockwise, should be $c-e=40, \, c=100, \, c-b=40, \,  c-(b+a)=100-90=10$ ft
A: If you look at the light area on your picture (which is supposed to represent where the cow can graze), you'll notice it's made entirely of quarter-circles of different radii. You should take a while and think about why the shapes would be circles.
Since you know how to find the area of a circle, you know how to find the area of the quarter-circle. All you need to do is figure out how large each of the radii are for each circle.
Here's a hint on how to start: The largest quarter-circle has a radius equal to the length of the rope, clearly. Now, what makes the radius smaller for the other quarter-circles?
