we have:
$15.50 -----> 100%
x --------------> 15%
then
[tex]\begin{gathered} x\times100=15.50\times15 \\ x=15.50\times\frac{15}{100} \\ x=15.50\times0.15 \\ x=2.325 \end{gathered}[/tex]so,
[tex]15.50+2.325=17.83[/tex]answer: $ 17.83 is the final bill