Recall that like terms are terms that have the same variables and powers. The coefficients of the terms do not have to match.
a.- Notice that 4z and -3z are like terms since they have the same variables with the same exponents, therefore:

b.- Notice that 3n and -3n are like terms, but 6 is a constant, therefore:

c.- In the given expression, the similar terms are 2g and -8g, and -3 and 11, therefore:

d.- In the last expression, first, we have to apply the distributive property:

Now, adding like terms we get:

Answer:
a.-

b.-

c.-

d.-
