Final answer:
Given that y is directly proportional to x with y = 6 when x = 18, we find the proportionality constant k = 1/3. The function representing the relationship is y = (1/3)x. We solve for x when y = 4, getting x = 12.
Step-by-step explanation:
To solve the mathematical problem completely regarding the direct proportionality of two variables, we must first determine the proportionality constant. Given that y is directly proportional to x and that for a value of x = 18, y = 6, we can set up the equation as y = kx. To find the constant of proportionality k, we use the provided values:
y = kx
6 = k × 18
Solving for k gives us:
k = 6 / 18
k = 1/3
With k determined, our function that represents the relationship between x and y is:
y = (1/3)x
Now we can find the value of x when y is 4:
4 = (1/3)x
x = 4 / (1/3)
x = 4 × 3
x = 12
Therefore, the value of x when y equals 4 is 12.