8. When you’re making subsets, you have two options for each element in the original set: you can either include it or not. This gives you 2 x 2 x 2 = 8 possible ways you can put a subset together from the three elements in {3, 4, 5}.
K, you have 2 minutes, one minute for one kilometer.
If you're in 60km/h, you're on 1km/m, so, if you cover 1 km in one minute, you need to stay in that speed to get to the train station.
She has 10 liters left. Find 4/9 of 18 by multiplying 4/9 and 18. 4/9 of 18 is 8, so she served 8 of the 18, leaving 10 liters.
