[R] how to get inflection point in binomial glm

[René Mayer]

Dear All,

I have a binomial response with one continuous predictor (d) and one  
factor (g) (8 levels dummy-coded).

glm(resp~d*g, data, family=binomial)

Y=b0+b1*X1+b2*X2 ... b7*X7

how can I get the inflection point per group, e.g., P(d)=.5

I would be grateful for any help.

Thanks in advance,
René