Residual Income: Terminal value of continuing RI (decline to LT level)

For this equation we’re supposed to calculate the terminal value as:

(Pt - Bt) + Rit / 1 + r

Where PT = Bt * (forecasted P/B)

Is there a different way to calculate PT or forecasted P/B? I was thinking I could use Bt * (ROE - g / r - g) but Im not sure this works…