Forfeiture amount per share is the amount to be received by the company on forfeiture of each share.
$$Forfeiture\quad Amount=Application\quad Amount\quad +\quad Allotment\quad Amount$$
Substitute the values in the above equation
$$Forfeiture\quad Amount=Rs30\quad +\quad Rs30\quad =\quad Rs60$$
Forfeiture amount is the money received by the company on forfeiture (cancellation of share) or on the reissue of share.
$$Forfeiture\quad Amount= No.\quad of\quad shares \times Forfeiture\quad Amount$$
Substitute the values in the above equation
$$Forfeiture\quad Amount=50shares \times Rs60= Rs3,000$$
$$Forfeiture\quad Amount\quad for\quad 20shares=20shares \times Rs60=Rs1200$$
$$Forfeiture\quad Amount\quad on\quad reissue=\quad 20shares\quad \times \quad Rs50\quad =\quad Rs1000\\ $$
Profit on the reissue is the profit earned by the company when the forfeited shares are reissued
$$Profit\quad on\quad reissue=Forfeited\quad Amount\quad on\quad forfeiture$$
Substitute the values in the above equation
$$Profit\quad on\quad reissue=Rs1200-Rs 1000=Rs200$$
Hence, the profit earned on the reissue of shares is Rs $$200$$
Share forfeiture a/c $$Dr. Rs200$$
To capital reserve a/c $$Rs200$$