482.
1) 21 * (16-12) / 16*21 = (16-12) / 16 = 4 * (4-3) / 16 = (4-3) / 4
2) 51xy/ 17x = 3xy/x = 3y
3) 21*(56+4) / 21*(56-5) = (56+4) / (56-5)
4) 3*(x-5y) / 4*(x-5y) = 3/4
631.
1) -15a*(-56) / a*14*(-5) = -15a*(-4) / a*(-5) = -3*(-4) = 12
2) -2b * (-3) * 5 / 5 * (-3b) = -2b*-3 / -3b = -2
3) -3a * 13b / b * 1.3 * (-a) = -3 * 13 / 1.3 = -3 * 10 = -30
4) 22 * 3 / -6.6 = 22 / 2.2 = 10