you're absolutely correct.
each system is sold for $2150, that includes cost + markup, namely the markup is the surplus amount otherwise called "profit".
they sold 12 of those, 2150 * 12 = 25800
they had $4824.36 in profits from it, so if we subtract that from the sale price, we'll be left with the cost of all 12 systems
25800 - 4824.36 = 20975.64
that's the cost for all 12 systems sold, how many times does 12 go into 20975.64? 20975.64 ÷ 12 = 1747.97.
