Start off by finding 18% of 13.90.
18%=18/100=0.18
0.18(13.9)=2.5
An 18% tip would be $2.50.
Now, to find out if Lana has enough money, add $2.50 to $13.90 to find out the total amount she would leave. You get $16.40. Since $16.40>$15, the answer is no because the total cost including the 18% tip is greater than $15.