Solve the Problem $\frac { 1 } { 31 } \mathrm { hr }$

Solve the problem.
-An experienced accountant can prepare a tax return in 13 hours. A novice accountant can do the job in 18 hours. How long will it take them to do the job working together?

A) $\frac { 1 } { 31 } \mathrm { hr }$
B) $\frac { 234 } { 31 } \mathrm { hr }$
C) $\frac { 1 } { 234 } \mathrm { hr }$
D) $\frac { 234 } { 5 } \mathrm { hr }$