Hi!
Given:
10x - 2x
These are like terms because they have the same variable and exponent.
(For example, 10x and 2x^2 are NOT like terms because they have different exponents. Also, 10y and 2x are NOT like terms because they have different variables.)
Therefore, we can subtract the coefficients, 10 and 2.
10 - 2 = 8
8x is your answer.
For the second one, the like terms are 10x and 2x, since they have the same variable and exponent. -3y is not, since it has a different variable.
Therefore we can add the like terms:
10x + 2x = 12x
Now, we have the leftover -3y
12x - 3y