Choi Group sells padlocks. It reported an increase in net sales from $5\mathrm{.}2$ billion in $2017$ for $$5\mathrm{.}5$ billion in $2018,$ and an increase in gross profit from $$1\mathrm{.}7$ billion in $2017$ to $$1\mathrm{.}9$ billion in $2018.$ Calculate each year's gross profit pertcentage.