Study the following table and answer the question below.
| School name | Total number of students enrolled | Percentage of enrolled students who opted for Biology | Ratio of male to female students who opted for Biology |
| A | 900 | 30% | 7 ∶ 8 |
| B | 400 | 38% | 9 ∶ 10 |
| C | 1000 | 24% | 5 ∶ 19 |
| D | 800 | 18% | 5 ∶ 7 |
What is the ratio of the total number of male students to that of female students who opted for Biology in schools A and D together?
1
38 ∶ 31
2
21 ∶ 38
3
31 ∶ 28
4
31 ∶ 38