a) (2.51+3.217) - 1.324 = 5.727 - 1.324 = 4.403

b) 13.04 +(8.235 – 3.7014) = 13.04 + 4.5336 = 17.5736

c) 3.113 – (2.129 + 0.45) = 3.113 - 2.579 = 0.534

d) (181.21 – 98.32) – 23.654 = 82.89 - 23.654 = 59.236