when solving these types of equations, i usually use the phrase: criss-cross multiply, divide by the lonely guy lol
x=unknown number
15/100=x/9 solve for x
15*9=100x simplify
135=100x divide both sides by 100
135/100=x simplify
x= $1.35
x/100=12/200 solve for x
12*100=200x simplify
1200=200x divide both sides by 200
1200/200=x simplify
x= 6%
