Worthy of What the Flock!

Multiply the number of brothers in your family by 2
Add 3,
Multiply by 5,
Add the number of your sisters
Multiply by 10
Add the number of living grandparents
Subtract 150
The 1st digit of the remainder will be the number of brothers
The 2nd digit is the number of sisters
The 3rd digit will be the number of grandparents
:)