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

100 - (b * 8 - 50) = 30
100 - 30 = 70
70 + 50 = 120
120 : 8 = 15
100 - (15 * 8 - 50) = 100 - 70 = 30
b = 15/

9600 : (540 : d - 4) = 600
9600 : 600 = 16
540 :d -4 = 16
540 : 16 + 4 = 27
9600 : (540 : 27 -4) = 9600 : 16 = 600
d = 27.