a can do a piece of work in 15 days and b can do it in 15 days and c can do it 20 days . they started the work together and a leaves after 2 days and b leaves after 4 days from the beginning . how long will work lost ?
"2 / 15 + 4 / 15 + x / 20 = 1 x = 12 answer : c"
add(divide(subtract(const_1, add(multiply(subtract(4, 2), add(inverse(15), inverse(20))), multiply(add(inverse(20), add(inverse(15), inverse(15))), 2))), inverse(15)), 4)