Solve the Problem $\frac { 1 } { 12 } \mathrm { hr }$

Solve the problem.
-One maid can clean the house in 5 hours. Another maid can do the job in 7 hours. How long will it take them to do the job working together?

A) $\frac { 1 } { 12 } \mathrm { hr }$
B) $\frac { 35 } { 12 } \mathrm { hr }$
C) $\frac { 1 } { 35 } \mathrm { hr }$
D) $\frac { 35 } { 2 } \mathrm { hr }$