Question 189276
.
Let x = time it takes to deliver together
x/30 + x/40 = 1
x(1/30 + 1/40) = 1
Multiplying both sides by 120:
x(4 + 3) = 120
x(7) = 120
x = 120/7
x = 17.143 minutes
or
17 minutes and 9 seconds