Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Perpetrator | Location | Country | Killed | Injured |
| --- | --- | --- | --- | --- |
| Bryant, Martin John , 28 | Port Arthur , TAS | Australia | 35.0 | 23 |
| Unknown | Siquijor | Philippines | 32.0 | 0.0 ? |
| Wirjo , 42 | Banjarsari | Indonesia | 20.0 | 12 |
| Formentera, Arsenio | Palompon | Philippines | 17.0 | 0.0 ? |
| Hodeng | Kampong Tankulu | Indonesia | 16.0 | 01 1 |
| Gz | Gz | Iz | 100.9 | 100.9 |
| Salazar, Domingo , 42 | San Nicolas | Philippines | 16.0 | 01 1 |
| Unknown | Ternate | Indonesia | 15.0 | 04 4 |
| Basobas, Florentino | Quezon, Palawan | Philippines | 15.0 | 04 4 |
| Antakin | Kaningow | Malaysia | 15.0 | 03 3 |
| Pusok Anak Ngaik, 28 | Kampong Bukit Merah | Malaysia | 14.0 | 04 4 |
| Sz | Qz | Nz | 100.9 | 100.9 |
| Unknown | Borneo | Indonesia | 14.0 | 0.0 ? |
| Unknown | Gondang | Indonesia | 13.0 | 03 3 |
| Gray, David Malcolm , 33 | Aramoana | New Zealand | 13.0 | 03 3 |
| Kalinga Boli | Tagan | Philippines | 13.0 | 0.0 ? |
| Two unknown Men | Zamboanga | Philippines | 12.0 | 14 |
Question:
What is the average number of people killed with a Perpetrator of wirjo, 42?
Answer:
20.0