I would like a math/finance expert to help me to solve/build simple finance model. The model is based on sequence of repeated sell in loss " martingale". Let us assume that: Price of an item is 100$ per unit, Size of first trade is 10 units. Grid distance " every certain number of price increase " = 10$, Retracement ratio to reach breakeven is 20% " means in case the price retrace 20%, you reach no loss no profit situation". I need to build that in excel.. However, i need some help in the equation part. Also, in case of you pay a fixed charge for the broker. Let us say, 1$ per unit

Question

I would like a math/finance expert to help me to solve/build simple finance model. The model is based on sequence of repeated  sell in loss " martingale". Let us assume that: Price of an item is 100$ per unit, Size of first trade is 10 units. Grid distance " every certain number of price increase " = 10$, Retracement ratio to reach breakeven is 20% " means in case the price retrace 20%, you reach no loss no profit situation". I need to build that in excel.. However, i need some help in the equation part. Also, in case of you pay a fixed charge for the broker. Let us say, 1$ per unit