If x and y vary directly, and x = 12 when y = 3, what will be the value of x when y = 9?

 The required value of x is 36.

Step-by-step explanation:  Given that the variables x and y varies directly. Also, x = 12 when y = 3.

We are to find the value of x when y = 9.

Given that x and y varies directly. So, we have

where 'k' is the constant of proportionality.

Given that x = 12 when y = 3, so from equation (i), we have

Substituting the value of k in equation (i), we have

When y = 9, we get from equation (ii) that

Thus, the required value of x is 36.

391.6 is the correct answer

the answer for the second equation is (4,0)