How to define BOM with fixed consumption?

Dear Experts,

I have a factor that fixed consumption 10 + 5 x quantity for a child item, how should I define the BOM?

For instance to produce 1 item, it requires 10 + 5 x 1 = 15

but to produce 2, then 10 + 5 x 2 = 20.

this fixed value 10 is predefined but different for every items.