(a) \(35 – (20) = 35 - 20 = 15\)(b) \(72 – 90 = -18\)(c) \((- 15) – (- 18) = (-15) + (18) = 3\)(d) \((- 20) – (13) = – (20 + 13) = – 33\)(e)\( 23 – (- 12) = 23 + 12 = 35\)(f) \((- 32) – (- 40) = (- 32) + 40 = 8\)