Combine the like terms.

12z+ 15z+ 8z+ 25z+ 19z+ 11z=

suppose you had

12 apples + 15 apples + 8 apples + 25 apples + 19 apples + 11 apples

How many apples would you have?
What did you do?

Now instead of apples you have those little z's
How many z's do you have

To combine the like terms, you need to add the coefficients of the terms with the same variable. In this case, the variable is "z".

12z + 15z + 8z + 25z + 19z + 11z

To add the coefficients, you can simply add the numbers in front of "z".

(12 + 15 + 8 + 25 + 19 + 11)z

Now, you can add the numbers together:

(90)z

So the simplified expression is 90z.