Why do we need to use call in advance here? and where is the 20000 x 2 call in advance from? Thank you.

Exercise 9.4 Share issue with oversubscription (Adapted). On July 2019, Denman Ltd issued a prospectus offering 160 000 of its ordinary shares payable $1 on application, $1 on allotment and $2 to be called as and when required. When applications closed on 23 July, applications had been received for 240 000 shares, including one applicant for 20 000 shares who had paid in full. The directors allotted the shares on 24 July as follows. . 1. The applicant for 20 000 shares, who paid in full, was allotted 20 000 shares. 2. Applications for 20 000 shares were rejected and the application money was refunded. 3. The remaining applicants were allotted 7 shares for every 10 applied for. The excess! application money on these shares was to be applied in part payment of allotment money. All allotment money was received by 7 August. Required (a) Prepare journal entries in general journal format to record the share issue up to 7 August. 2019 July 23 Cash Trust 300 000 Application Cash received on application (20 000 $4) + (220 000 x $1) 300 000 24 Application (160 000 $1) Allotment (160 000 x $1) Share Capital Amounts receivable on application and allotment. 160 000 160 000 320 000 24 Application 140 000 Calls in Advance (20 000 $2) 40 000 Allotment (20 000