Question 767587
How about anything that fits this:


m men can build a wall in d days.  how many days will n men take to build the same wall?


Variables are:
m = number of men for a defined job
d = number of days for the defined job
n = number of men different than m, {{{n<>m}}}.


CALCULATE THE WORK RATE FOR ONE MAN.
The defined group of men need d number of days, so if only 1 man is available, he needs m times as many days to do the job.  This means the one-man rate is 1 man needs {{{d*m}}} days.  
His rate can be expressed as {{{1/(d*m)}}} jobs per day.


RATE FOR A DIFFERENT NUMBER OF MEN.
Now, you want the rate for some other number of men; the quantity, n men.  What is the rate now if n men are to do the job?  The rates are additive, so each man in the group contributes at 1/(d*m) jobs per day; and since we now have n men to do this job, the rate is:
{{{highlight(n(1/(d*m)))}}} jobs per day.


In your actual question you can find the given variables' values and just substitute them into the expression:
m=12; d=4; n=3.
{{{3/(4*12)=1/(4*4)=highlight(1/16)}}} jobs per day
That means 16 days needed for the 3 men to do the job of building this wall.