The frequency distribution of the age of students in a class of $40$ students is given below.

| Age | $15$ | $16$ | $17$ | $18$ | $19$ | $20$ |
|-|-|-|-|-|-|-|
| No. of Students | $5$ | $8$ | $5$ | $12$ | $x$ | $y$ |

If the mean deviation about the median is $1.25$, then $4x + 5y$ is equal to