Answer: It is only one can that can be filled up.
Step-by-step explanation: If 1 gas can can hold 10 L of gas and you only have 7 L then how can you fill up more than 1 gas can with only 7 L? You don't have enough gas to fill up more than 1 gas can. So you are left with only 1 gas can filled but only with 7 L.
The easiest way to think about this is to give all of the numbers common denominators:
1 can be written as 6/6
0 can be written as 0/6
Now we can see that 5/6 is only 1/6 away from 1, while it is 5/6 away from 0.
So, 5/6 is closer to 1!
Alright, so [-2.99] is -2.99, and [2.99] is 2.99, so -2.99+2.99=0