if 5 % more is gained by selling an book for $ 350 than by selling it for $ 340 , the cost of the book is :
"c 200 let c . p . be $ x . then , 5 % of x = 350 - 340 = 10 x / 20 = 10 = > x = 200"
divide(subtract(350, 340), divide(5, const_100))