Dale and Kim can assemble a swing set in 1 1/2 hours.Working alone it takes kim 4 hours longer than Dale to assemble the swing set .How long does it take Dale working alone to assemble the swing set?
1/d + 1/(d+4) = 1/(3/2)
d+4 + d = 2/3 d(d+4)
6d + 12 = 2d^2 + 8d
2d^2 + 2d - 12 = 0
d^2 + d - 6 = 0
(d+3)(d-2) = 0
d = 2
1/2 + 1/6 = 1/(3/2)
works for me