11.25cups. I got that by multiplying 2.5. by 4.5. If she wants to make 4.5 batches and 1 batch uses 2.5 cups, you have to multiply the cups of 1 batch by the number of batches she wants to make.
Add (11/2)^2 to both sides
x^2 + 11x + (11/2)^2 = 3 + (11/2)^2
x^2 + 11x + (11/2)^2 = 133/4
(x + 11/2)^2 = 133/4
x + 11/2 = sqrt of (133/4)
Solutions are
x = (sqrt of (133) - 11))/2
x = (-sqrt of (133) -11))/2
It can be many things such as,
420/2
630/3
840/4
