How do you find the domain of #y=4x+2#?
The domain is all real numbers.
Domain is what the x-value can be without the y-value becoming undefined. In this instance, no values of x will make the y value something imaginary, so all real numbers is the domain. Pay attention to the real part of that, because, depending on teachers, you can get it marked wrong on a test.
If you're ever unsure, you can try graphing it. That'll normally show you if the domain is restricted.