First of all, x/3 means to divide.
To solve, you need to add 4 and 5 together to find what you need to subtract from 4 to get 5. The answer is 9.
You then multiply 9 by 3 to find x since you have to divide 3 by x to make the problem true.
You get 27 as x since 27 divided by 3 is 9 and 9 minus 4 is 5 so that all works out.