What equation can be used to find the measure of an angle that is supplementary to angle EOF?

To make an equation, make angle EOF = X and the angle that is supplementary to angle EOF = Y

An angle that is supplementary to another angle means that when you add the two angles, it equals 180 degrees.

So no matter what,

X + Y = 180

But the question asks us to find the angle that is supplementary to X, not what X plus the supplementary angle is equal to.

So to find that angle:

Y = 180 - X is the answer