we know that
A relationship between two variables, x, and y, represent a proportional variation if it can be expressed in the form
y=kx
where
k is the constant of proportionality
step 1
Find the value of k
we have that
For x=75 y=15
substitute the given values
15=k(75)
solve for k
k=15/75
simplify
k=1/5
step 2
Find the value of y when the value of x=30
we have the equation
y=kx
substitute the value of k
y=(1/5)x
For x=30
y=(1/5)30
y=6