Where r is the corner radius on the punch?

Question

For calculating the blank diameter D for thin cylindrical shell of outer diameter d and with height of the shell h, which one of the following formulae is used when d $\geq$ 20r, where r is the corner radius on the punch?

(a) $D=\sqrt{d^{2}+4dh}$                                                   (c) $D=\sqrt{d^{2}+4dh-0.5r}$

 (c) $D=\sqrt{d^{2}+4dh-r}$                                                (d)$D=\sqrt{d^{2}+4dh-1.5r}$