a can do a piece of work in 21 days and b in 28 days . together they started the work and b left after 4 days . in how many days can a alone do the remaining work ?
"let a worked for x days . x / 21 + 4 / 28 = 1 = > x / 21 = 6 / 7 = > x = 18 a worked for 18 days . so , a can complete the remaining work in 18 - 4 = 14 days . answer : d"
add(divide(subtract(const_1, add(multiply(4, divide(const_1, 21)), multiply(4, divide(const_1, 28)))), divide(const_1, 28)), 4)