Respuesta :

If you think about it, x=12 when y=3, right?
So the function is going to be f(x)=y*4
So, if y = 9 and you put it in the function, x is going to equal 36. 
Do this help you understand?

Answer:  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

[tex]x\propto y\\\\\Rightarrow x=k~y,~~~~~~~~~~~~~~~~~~~~(i)[/tex]

where 'k' is the constant of proportionality.

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

[tex]x=k~y\\\\\Rightarrow 12=k\times 3\\\\\Rightarrow k=\dfrac{12}{3}\\\\\Rightarrow k=4.[/tex]

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

[tex]x=4y~~~~~~~~~~~~~~~~~~~~(ii)[/tex]

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

[tex]x=4\times 9\\\\\Rightarrow x=36.[/tex]

Thus, the required value of x is 36.