PHYSICS PLEASE HELP ASAP
posted by Laila on .
When an object is placed 55.0cm from a certain converging lens, it forms a real image. When the object is moved to 45.0cm from the lens, the image moves 6.00 cm farther from the lens.
Find the focal length of this lens?
Please someone help me out I tried so many times i keep getting wrong answer.

1/f=1/di+1/do
f=dido/(di+do)
but f before the move is f after the move, so
(di+6)(55+45)/(di+55+51)=di55/(di+55)
solve for di. Looks like fun.
then, after you get di, go for f from the lens equation 
I found this equation 5380di^2+600di+33000=0 and when i solve i got an imaginary number I had a hard time solving it so could you please help me out