Problem Solving

A marketing firm determined that, of 200 households surveyed, 80 used neither Brand A nor Brand B soap, 60 used only Brand A soap, and for every household that used both brands of soap, 3 used only Brand B soap. How many of the 200 households surveyed used both brands of soap?

According to Mantn. I made a Double chart resulting in 3x=60+x so X=30.
But the explanation says 3x+x=60 so x=15. Anyone who can explain this?
Many tks