Question 1126439
he starts with 100 liters.
he will top up when there are 20 liters left in the tank.
that means he will top up when he consumes 80 liters.
if he uses 8 liters a day, then he can go 10 days before topping up again.


your formula can be:


20 = 100 - 8x


x is the number of days before he needs to top up again.


solve this equation for x as follows:
add 8x to both sides of the equation and subtract 20 from both sides of the equation to get:
8x = 100 - 20
combine like terms to get 8x = 80
divide both sides by 8 to get x = 10.