a/30.x=2280040
30.x=570
x=570:30=19
b/(x.30):40=840
x.30 =840.40
x.30 =33600
x =33600:30=1120
c/37200:x=60.5
37200:x=300
x=37200:300=124
d/(72000:x):60=5
72000:x =5.60
72000:x =300
x =72000:300=240