Answer:
-2x
Step-by-step explanation: A like term has the same variable and exponent. For example 3x^4 and 3x^3 are not like terms because they have different exponents and 3x^4 and 3y^4 are not like terms because they have different variables. In 4x-6x they are like terms. When you add or subtract like terms the variable and exponent stay the same so you only need to worry about the numbers out front which in this are 4 and 6. So when you have positive 4 and take 6 away you end up with -2 and since the variables and exponents stay the same you just add them back onto it and end up with -2x.