There are 5 tons of steel in a warehouse, 15 of the total is used for the first time, and 15 tons are used for the second time, how many tons of steel are left?
某仓库有小5吨钢材，第一次用去总数的15，第二次用去15吨，还剩钢材多少吨？
<result>19.8</result>