plz help

Okay so first some definitions

Geometric sequence and common ratio. A geometric sequence a sequence where the next number is the previous number multiplied by the same number as in the whole seequence a.k.a a common ratio.

equation:

 $\frac{150+c}{120+c}=\frac{120+c}{60+c}=x$

okay so we want to find  what x is.

solve: find common denominators

$9000+210c+c^2 = 14400+240c+c^2$

$30c=-5400$ , so$c=-180$. 

Now we get x = 1/2 $so$ yeah

TO CHECK: 

plug x back in to the equations to that it is correct! I hope you got it so the common ratio is $\boxed{1/2}$