Question 983388
Do you know how to perform polynomial division?

You have {{{A=5x^2+19x+12}}}, and {{{w=5x+4}}};
if your length is L, then {{{wL=A}}}.


Solving the formula for L, you have {{{L=A/w}}}.
This means A divided by w.  


Now, with that discussed, and hopefully understood, if you know polynomial division, then do it.  If not, I will help with the polynomial division.