Question 978100
{{{y=(2(2y+5)-3)((2y+5)+9)}}}, the substitution for x.
{{{y=(4y+10+5)(2y+5+9)}}}
{{{y=(4y+15)(2y+14)}}}
{{{y=8y^2+30y+4*14y+15*14}}}
{{{y=8y^2+86y+210}}}
{{{0=8y^2+85y+210}}}


Find the solutions for y, which might be none, or one, or two of them.


I CHOSE to make the substitution for x instead of for y.  You could just as well make the sub for y as you may have wanted.  My view is that the subst for x is easier to use.


What you actually tried to do is tougher, and may be more work.