its really hard for me to do this

To solve for b you will want to get it to one side of the equation

6+3b=-18

Let's start by subtracting 6 from both sides.

3b=-18-6

Now you can simplify those number on the right.

3b=-24

Now to get b by itself you will need to divide by the 3 on both sides.

So, after simplifying, b will equal -8.