How much of a 60% saline solution would you need to add to pure water to create 10 l of a 50% saline solution ?

So say, we add "x" of the 60% saline solution, now, how much salt is in that solution?  now 60% is salt but the rest is something else, but only salt is 60% of "x", or (60/100) * x, or 0.6x.

likewise, for the 10 Liters, if only 50% is salt, then is just (50/100) * 10 or 5.

now... let's check the water whilst we add "y" amount, the water has no salt at all, freshwater for that matter, so, salinity is 0%.  or (0/100) * y or 0.