Like terms have the same variables, in this case, for the expression 3b + 4 - 2b + 10 we can identify two groups of terms, those with the variable b (3b and -2b) and those that are just numbers (4 and 10), to simplify this, then perform the subtraction 3b - 2b and the sum 4 + 10, like this:
3b - 2b + 4 + 10 = 1b +12 = b + 12
Then, the result is b +12