If the question is this: 7+18÷3, than you would have to use PEMDAS, the order of operations. So, you would divide 18 by 3, which is 6, and then add it to 7, which is 13.
However, if the question is asking you to add 7 and 18 first, then you have to do that, which is 25, and then divide that by 3, which is 8 [tex] \frac{1}{3} [/tex].