To find the answer to this, we must first understand what exactly the sentence says. First of all, let's identify some words that may give us some hints as to what operations we need to use.
more - this means we'll use addition.
one third - this means we'll have to divide by 3.
First of all, let's figure out what seven LESS than 18 is. Very simply, we know that it's 11.
Now, all we must do is multiply be 3. 11 x 3 = 33.
Final Answer : 33
Hope this helped. :)