To solve for x when y is 9, we start by understanding that x and y vary directly. This means there is a constant ratio between the values of x and y. We can express this relationship as:
y = k * x
where k is a constant. From the information given, we know that:
x = 12 when y = 3
Now, we need to find the value of k:
3 = k * 12
Solving for k gives us:
k = 3 / 12 = 1/4
Now that we have the constant k, we can find the value of x when y is 9:
y = k * x
Substituting y = 9 and k = 1/4 into the equation:
9 = (1/4) * x
To solve for x, we can multiply both sides by 4:
36 = x
Thus, when y is 9, the value of x is 36.