Multiply both sides by D:
Do the multiplication on the right and subtract QD from both sides:
Now that is a fourth degree equation. There is a "formula" for solving general fourth degree equations but it is very complicated:
Quartic function - Wikipedia, the free encyclopedia
Thanks for help guys. Didn't realise the WA was a hyperlink, thanks.
After looking into the 4th degree equation I found the equation must be in the format:
ax^4 + bx^2 + c=0
In my equation the middle part is not squared so I cannot solve the equation.
I am beginning the think the equation cannot be rearranged simply for D and the only answer for it is on WA provided by princeps