25*9*b*4 96*7+4*7 57+b+43+ b 89*6-9*6 72*5+28*5.

25 * 9 * b * 4 = (25*4*9)b = (100*9)b = 900b
96 * 7 + 4 * 7 = 7 * (96 + 4) = 7 * 100 = 700
57 + b + 43 + b = (b + b) + (57 + 43) = 2b + 100
89 * 6 - 9 * 6 = 6 * (89 - 9) = 6 * 80 = 480
72 * 5 + 28 * 5 = 5 * (72 + 28) = 5 * 100 = 500