4. a ) 4 × 67 × 25 = 67 × ( 4 × 25 ) = 67 × 100 = 6 700
b) 50 × 145 × 2 = 145 × ( 50 × 2 ) = 145 × 100 = 14 500
c) 4 × 315 + 6 × 315 = 315 × ( 4 + 6 ) = 315 × 10 = 3 150
