Remember you can only add x's together if they have the same power. This makes sense why you can 2 to -1 because they are both the same power of x, x^0. (which equals 1 by default)
Because the total is 49.77 and the total is the bill + tip, then the tip is 49.77 - 42 or $7.77. To find the percentage, we just calculate 7.77/42 as a percentage to get 1.11/6 = (111/6)% or 37/2 percent or 18.5%
