100-(b*8-50)=30
9600:(540:d-4)=600

100 - (b * 8 - 50) = 30100 - 30 = 7070 + 50 = 120120 : 8 = 15100 - (15 * 8 - 50) = 100 - 70 = 30b = 15/9600 : (540 : d - 4) = 6009600 : 600 = 16540 :d -4 = 16540 : 16 + 4 = 279600 : (540 : 27 -4) = 9600 : 16 = 600d = 27.