а) 0.4 ⋅ 5a ⋅ 0.7 = (0.4 ⋅ 5 ⋅ 0.7)a = 1.4a
б) 0.5 ⋅ 0.6b + 0.5 ⋅ 0.4b = 0.3b + 0.2b = 0.5b
в) 0.3s ⋅ 0.21 - 0.21 ⋅ 0.2s = 0.063s - 0.042s = 0.021s
г) 0.99 ⋅ 0.25t + 0.0025t = 0.2475t + 0.0025t = 0.25t
Ответ: а) 1.4a; б) 0.5b; в) 0.021s; г) 0.25t