The following figure shows the data of students enrolled in $5$ years $(2014 to 2018)$ for two schools $P$ and $Q$. During this period, the ratio of the average number of the students enrolled in school $P$ to the average of the difference of the number of students enrolled in schools $P$ and $Q$ is _______.

1. $8 : 23$
2. $23 : 8$
3. $23 : 31$
4. $31 : 23$

edited

Total number of students enrolled in school P:   $3K+5K+5K+6K+4K=23K$
Total number of students enrolled in school Q:  $4K+7K+8K+7K+5K=31K$
Difference between the number of student enrolled in school P & school Q :  $31K-23K=8K$
Required ratio :  $\frac{23K}{8K}$