a) 4/63 + 1/18 - (2/5)^2 × 5/7 = = 2×4/126 + 7/126 - 4/25 × 5/7 = = 15/126 - 4/35 = = 5/42 - 4/35 = = 5×5/210 - 4×6/210 = = (25-24)/210 = = 1/210 b) ( 1 + 3/2 × 5/2) : 6 - 1 = (1 + 15/4) × 1/6 - 1 = = (4/4 + 15/4) × 1/6 - 1 = = 19/4 × 1/6 - 1 = = 19/24 - 1 = = 19/24 - 24/24 = = (19-24)/24 = = - 5/24