Answer :
He left $4.50. You just find 15% which is 10% and then 5% added on.
[tex]multiply\ 15\%\ by\ a\ cost\ of\ bill\\\\
15\%*30=\frac{15}{100}*30=0,15*30=4.5\\\\
He\ left\ 4.5\$\ for\ tip.[/tex]