So it's good to map out what you know you have and work from there:
We have two liter measurements and one mole measurement, and we need to find the moles.
For this problem, think of it this way: 46 liters of gas = 1.4 moles.
If one side changes, the other has to as well (if the liters decrease, the moles decrease. if the liters increase, so do the moles.) What you can do is put this into a fraction:
1.4 moles
46 L
if we know that each liter of gas is equal to x amount of moles, we know that 11.5 liters equals some amount of moles. You can put this into a fraction too, and make it equal to the other fraction:
1.4 moles = x moles
46 L 11.5 L
Then get your calculator out and do some algebra.
11.5 * (1.4/46) = x
The answer should come out to be: 0.35 moles
