Question 970280
Here is just a start.

{{{system(L=48+3w, wL=1260)}}}


{{{w(48+3w)=1260}}}


{{{3w^2+48w-1260=0}}}


{{{w^2+16w-420=0}}}


Discriminant is {{{1936=44^2}}} and this means you expect to find integers solutions.


{{{w=(-16+- 44)/2}}} and you accept only the positive solution for w.
{{{highlight(w=14)}}}