Question 1000081
The walls is a separate job than the ceiling; otherwise the description would not be very clearly understandable.  Try assuming that Jenny and Martha work on one job at the same time, finish it, and then do the next job, also at the same time.


The sum of their individual rates is their effective combined rate on each job.


WALLS
{{{(1/(3/2)+1/1)*t[w]=1}}}


CEILING
{{{(1/2+1/1)*t[c]=1}}}


Examine how the described rates are placed into those two equations.  The time IN HOURS to do BOTH JOBS is  {{{t[w]+t[c]}}}.