Answer:
x = 100
Explanation:
First, you start with putting either 10 liters ontop of 40 km or the other way around. Then, whichever place you put the 10 liters, you put the 25 on the opposite side. Then the missing km is the 'x'. You need to do cross-products. So, it would be like this: 10x = 40 * 25. You start with 40 times 25, which is 1,000. Then divided by 10 on both sides. Which would take out the 10, which would be left with the 'x', and divide 1,000 by 10 it would be 100.
I hope this helps! My apologies if it's wrong. I'm not good with math.