Dominic has $ 15 for dinner. his meal cost $13.90 he wants to leave an 18% tip. does he have enough money

I don't know.  Let's figure it out and see.

18% of $13.90 means  (0.18) x ($13.90)  =  $2.50

Add the tip to the bill:    ($13.90) + ($2.50) = $16.40  .

Sadly, Dominic does not have enough money to leave an 18%  tip.
He only has enough money to leave a  7.9%  tip.

This doesn't hurt Dominic.  He leaves the restaurant happy and well fed.
The only one who suffers for Dominc's inconsiderate failure to think ahead
is the waiter who served him his dinner.

What do you mean by that?

It says in the questions that it is 6.5?