My homework is about combining like terms to simplify so i don't understand 1 problem so i need
here's the problem
18-4y-11+20

So, to solve this problem you just need to combine the variables, and the constants (integers).  

The first thing you should do is combine 18 and -11, which equals 7.  So, instead of writing 18-11, you can write 7.
Your equation now is 7-4y+20

Now you can combine 7 and 20, which is 27.

Your final answer is 27-4y or -4y+27.