C. The total area of the patio.
If you don't know the area you can't know how many bricks you need.
Since C is 61 degrees, A is 90 degrees because of the right angle, and B would be 29 degrees because you add 61 and 90 together and subtract that amount from 180.
Wait I'm sorry if this is what you aren't looking for-
The discriminant is b²-4ac
when the discriminant is 0, there is only one solution.