A jeweler has 4 rings, each eighing 19 g, made of an alloy of 15% silver and 85% gold. He decides to melt down the rings and add enough silver to reduce the gold content to 78%. How much silver should he add?
_________ g silver

You could re-word this problem to make it a little more palatable.

"How much pure silver should be added to 76 grams of an alloy that is 15% silver in order to get an alloy that's 22% silver?".

Let s = the amount of pure silver to be added.

Can you continue? Write back if you're still stuck.

If the gold content changes from 85% to 78%, then what will be the new percentage of silver? Determine that proportion of 19g, then multiply by 4. Next, calculate how much silver is in the rings currently (15% of 19g times 4), then subtract. The difference is the amount of silver that needs to be added.