Apparently, we are to presume the cost of the pizza is proportional to its area. The ratio of areas is proportional to the square of the ratio of diameters. Hence we expect a 20" pizza to cost
(20/12)² × $7.95 ≈ $22.08
You can only add/subtract like terms so:
2a+ab+2b+4a^2-3ab+9
2a-2ab+2b+4a^2+9 (the only like terms were ab and -3ab)
Square root is the number that when multiplied when itself give the number you are looking for if that makes any sense.
8 is the square root of 64 because 8x8 = 64
