x²-21.75x=-15.75 multipy through by 100 to clear the decimals
100x^2 - 2175x = -1575 add 1575 to both sides
100x^2 - 2175x +`1575 = 0 divide by 25
4x^2 - 87x + 63 = 0 factor
(4x - 3)(x - 21) = 0 and setting each factor to 0, we have that x = 3/4 or x = 21
