What is the zakat rate due on a mortgaged sum of money that has been entrusted to a merchant to invest for three years, with a percentage of its profits to be received?

If the amount reaches the nisab and is invested in trade, then at the end of each hawl (lunar year), the principal and its profits are calculated, and debts are deducted. What remains, if it reaches the nisab, then a quarter of a tenth (2.5%) is to be given as Zakat; otherwise, there is no Zakat due on it. Zakat must be disbursed immediately upon its due date. To compensate for past years, Zakat is calculated for each year separately if the wealth reached the nisab in that year.