Someone wrote this formula but i couldn't make sense of it. Please help me.

First formula, "=vlookup(quantity, base, 2 true) - picks up from quantity
and base table.
Second Formula = vookup(quantity, multipler, 2 true)-picks up from
multipler table
Third formula = if(Quantity 1000, Quantity-I4, if (Quantity=500,
Quantity-I4 ......)))

The issue is "I4 returns $ value from the base table for quantities from
1-20 kgs. "J4 returns Multiplier value in $ from multiplier table for
anything than 20 Kgs. "K4 returns as "I4-Quantity".

For an example; I4 returns $ value for anything below/equals 20 kg (picking
up from the base values) than minuses out any quantity than 20 kg from the
total quantity in question and returns in cell K4. Can you do that?? Dollar
value minus quantity!!! After that K4 multiply by the multiplier(J4) in $
value.

The Final Formula reads : I4*J4 + (K4*J4). Is this possible???