$75 -----> 100%
x ---------> 20%
[tex]\begin{gathered} x\times100=75\times20 \\ 100x=1500 \\ \frac{100x}{100}=\frac{1500}{100} \\ x=15 \end{gathered}[/tex]asnwer 1: they leave her $ 15
answer 2: the total cost of the meal is
[tex]75+15=90[/tex]$ 90