1 + 5*13 = 18 is obliviously not true so that takes out the first option.
13 + 5*1 = 18 : This is true but we have to check the next one. 13 - 3*1 = 10 : This is also true so we know this is the answer. We don't really need to check the other 2 but u can if u want to.
