a) x/100 = 15/90x = 100(15/90)
x = (10/9)15
x = 10*(5/3)
x = 50/3
x = 16.667
x = 16% or 2/3
b)56/x=100/10(56/x)*x=(100/10)*x
56=10*x
56/10=x
5.6=x
x=5.6
c)180/x=100/90
(180/x)*x=(100/90)*x
180=1.11111111111*x
180/1.11111111111=x
162=x
x=162
d)300/x=100/25
(300/x)*x=(100/25)*x
300=4*x
300/4=x
75=x
x=75
f)20/x=100/55
(20/x)*x=(100/55)*20
x=36.36
x=36
I don't know how to do e), sorry.