The correct answers to this question are:
Add -3.6 to both sides
and
Subtract 3.6 from both sides.
This is because to solve any equation, we need to get the variable by itself on one side of the equation. The only way to do this in one step in the example above is to eliminate the +3.6 term on the left side of the equation. To do this, our two options are to add -3.6 or to subtract 3.6 (because these are technically the same operation).
Hope this helps!