* Kendra and her family used:
** 4 liters of fuel on day 1
*** 3 liters of fuel on day 2
**** 2 liters of fuel on day 3
***** 4 liters of fuel on day 4
So in total they used:
4 + 3 + 2 + 4 = 13 liters of fuel
Therefore, the amount of fuel they used in all is:
13 liters