use of root() with 3 parameters - how to?

to all

i wnat to use the root() optin to solve a "simple" 2nd order equation. The 1st pass works fine but I now would like to set it up so that root() give me a set of x values for a set of given parameters. Please see attahce dmcad sheet

the equaqtion is as follwos

          a(A,B,t)x^2 + b(A,B,t)x + c = 0

I can solve it if I set values for say A and t

Thanks

Regards

JXB