PLEASE HELP
when x=21, y=5. find x when y=25

This is a simple ratio. x : y.  So x = 21 when y = 5.

21 : 5.

x : 25

So you are timesing each side by 5

So 21 x 5 = 105.

x = 105

when x is 21 and y is 5 means that y*4.2=x ( bc 21:5=4.2) so to find x u have to multiply y*4.2

Step-by-step explanation:

21/5 = 4.2

25*4.2 = 105

the revenue of the fitness center, y, is the product of two factors: the number of members and the fee paid by each member. there are 320 members now, but number of members goes down by 10 for each $5 increase in fees, so if x is the number of $5 price increases then members is equal to (320 - 10x). since the fee is currently $45, and the fee increases by $5 for every price bump x, the fee is given by (45 + 5x). so, revenue y is given by y = (320 - 10x)(45 + 5x).