Function break_infinity::sum_geometric_series

pub fn sum_geometric_series(
    num_items: &Decimal, 
    price_start: &Decimal, 
    price_ratio: &Decimal, 
    current_owned: &Decimal
) -> Decimal

How much resource would it cost to buy (numItems) items if you already have currentOwned, the initial price is priceStart and it multiplies by priceRatio each purchase?