So we know that there are 1000 mL in 1 L. We can set up an equation that allows us to solve for how many bottles are needed in order to empty the 30 L tank:
![(1 bottle)/(350 mL)* (1000 mL)/(1 L)* (30 L)/(1 tank)](https://img.qammunity.org/2019/formulas/mathematics/middle-school/t9jirxhh8rc686tldj203fli5s6fcaevw7.png)
This equation then allows us to cancel out the units of mL and L, leaving us with how many bottles are needed per tank. Then we multiply straight across to give us:
![(30,000)/(350)= (85.71 bottles)/(1 tank)](https://img.qammunity.org/2019/formulas/mathematics/middle-school/fdd2end0f4ta0aw8g14kta636rwe5uw6m1.png)
The question asks us to round up to the next whole number, so
it would take 86 bottles to empty one 30 L tank.