A function will only have that property if it’s a line that passes through the origin. For example, *f*(*x*) = 5*x* has that property:

You can try the same with other linear functions to see why they won’t work. For example, if *f*(*x*) = 5*x* + 2:

Nonlinear functions also won’t work. For example, if f(x) = x^2:

Anyway, now that we know we’re dealing with a linear function through the origin, we can figure out that if *f*(6) = 12, then the function we’re dealing with must be *f*(*x*) = 2*x*. Therefore, *f*(2) = 4.

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