Q. How many litres of a solution that is 15% salt must be added to 5 litres of a solution that is 8% salt so that the resulting solution is 10% Salt.

ok so we have 0.15x + 5(0.08) = 0.08 (x+5).

I completely understand all the above, until the (x + 5). Why do we need to multiply the 8% by x + 5?

Thanks a million.