a marketing firm determined that , of 200 households surveyed , 80 used neither brand k nor brand b soap , 60 used only brand k 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 ?
solution for soap k and soap b ( d ) 40
divide(subtract(subtract(200, 80), 60), add(3, const_1))