Explanation:
Let the size of their father's land be x.
The first born received x/4
The second, third and fourth born each received 1/6 * (x - x/4) = 3x/24 = x/8
The portion received by the last born = x - (x/4 + 3*x/8) = x - (x/4 + 3x/8) = x - (5x/8) = 3x/8
3x/8 = 3hectares
3x = 24
x = 8.
. : The initial size of the parcel land was 8 hectares.