Remark
This is sort of like a problem using d=r*t. The formula would be somewhat the same.
Givens
t = 2 1/2 hours
C = Cups of coffee = 2 3/16
R = ??
Formula
C = R * T
Solution
2 3/16 = R * 2 1/2 Change to decimals
2.1875 = R * 2.5 Divide both sides by 2.5
R = 2.1875 / 2.5
R = 0.875 cups / hour
That's the same thing as 7/8 cup (just run through the answers with a calculator if you are not sure where that comes from).