Answer:
The answer is

Explanation:
From the question
 is inversely proportional to 
 is written as

where k is the constant of proportionality
When 
 = 4
 = 9
Substituting the values into the formula 
we have

cross multiply
k = 4 × 9
k = 36
So the formula for the variation is
 = - 72
That's

Simplify
We have the final answer as

Hope this helps you