If `x%` of 50= `y%` of 60 then `x:y=`

x% of y is y% of ?

What should come in the place of question mark (?) in the following questions ? If x% of 500 =y% of 300 and x% of y% of 200=60, then x= ?

x% of 800 is 10 then x=

. If 80% of A = 50% of B and B = x% of A then x=

x% of 360=72 then find x