What is 4x plus 2y equals 1?

Answer 1

It's a simple linear equation in two unknowns.

If you want to know what value of 'x' or 'y' makes it true, you'll need another equation.
You always need as many equations as there are unknowns.

From the single equation given in the question, we only know these two things:

-- whatever 'x' is, 'y' is [double it] less than 1/2

-- whatever 'y' is, 'x' is [half of it] less than 1/4