Yand x have a proportional relationship, and y = 15 when x = 3. what is the value of x when y = 4?

In a proportional relationship, x and y will increase at the same rate. In order to find the value of x when y=4, we first have to find the ratio of x:y. We can do this by creating a fraction. After we know the ratio, simply replace the y value with 4 and solve for x. Here's the math:

y=15 when x=3       given values

y/x = 15/3 = 5          ratio of y to x

y=5x                        equation representing the proportional relationship 

4=5x                        replace y with 4

4/5=x                       divide both sides by 5 to isolate x

 The value of x=4/5 when y=4.

Hope this helps!