Based on the information given, 3 5x can at best be read as 15x = 18, which would imply that 18/15 is the answer, but it cant be. So im assuming you forgot to put a sign there.
Lets first test with a + sign.
18 = 3+5x can be solved like this:
18-3 = 5x
15 = 5x
3 = x
Which is a legal answer.
Then we test with a - sign.
18 = 3-5x can be solved like this
18+3 = 5x
21/5 = x
Which isnt a legal answer in this context.
Hence ive come to believe 3 is the answer you are looking for :)
