15.
[tex]3x-5+2x=90\\ 5x=95\\ x=19[/tex]
16.
[tex]\$38.85-\$6=\$32.85\leftarrow\text{this much they spent without the tip}\\
\$32.85\div3=\$10.95\leftarrow\text{this much paid each of them}\\
\$10.95+\$2=\$12.95\leftarrow\text{this is the regular price}\\[/tex]
