First of all, I think the first question lacks conditions. At least I need to know the speed of the dog or how many times it has run back and forth, otherwise I can't have it.

Question 2: A discharges 60 * 4/5g of salt and 60 * 16/5g of water per minute.

B 60 * 6/20g salt 60 * 1 12/20g water flows out every minute.

C 60/(2+5) = 8+4 (no flow for 2 seconds), so running water for 42 seconds * 10g = 420g.

Salt content is 240/5+360/20 = 66g, and water content is12 *16+3 *1kloc-0/2 = 528g.

So the salt content is 66/(66+528) =11.1%.