Answer:
3.6 hours
Step-by-step explanation:
To determine the time needed if they are working together, we use the formula
1/Ta + 1/Tb = 1 Tc
where Ta is the the time for the first item working alone
Tb is the time for the second item alone
Tc is the time for them working together
1/9 + 1/6 = 1/Tc
I multiply by 54Tc to clear the fractions
54Tc (1/9 + 1/6) = 1/Tc *54Tc
6Tc + 9 Tc = 54
Combine like terms
15Tc = 54
Divide each side by 15
15 Tc /15 = 54/15
Tc =3.6 hours
