Question 864843
This one and your other one could be both solved symbolically first, which I will do here.


A = area of the rectangle.
x for length
y for width,
x=k+m*y, where k is a positive real number and m is a positive real number factor.
In the current problem, k=5 and m=1.  Also A = 104.
The unknown variables are x and y.


{{{A=xy}}}, equation for area.
{{{A=(k+my)y}}}
{{{my^2+ky=A}}}
{{{my^2+ky-A=0}}}
-
{{{highlight(y=(-k+- sqrt(k^2-4*m(-A)))/(2m))}}}
Note that this will often give two values for "y" but only one of these values has any practical meaning; and will the the POSITIVE solution.  Also note this solution is for "y", here taken as the "width".   You will need to return to {{{x=m*y+k}}} to compute  x, the length.


Be aware that if you use the given values from the very start instead of solving symbolically, you may find for "algebra 1" level rectangle problems of this type, that the quadratic expression is factorable.  You cannot see that when solving first in purely symbolic form.