What is the method for calculating the Zakat on a sum of 100,000 Riyals invested in a warehousing project that yields an annual profit of 7,000 Riyals?

If the money paid was a loan with annual interest, then it is forbidden usury (riba), and you must repent. Only the principal must be returned, and it should be Zakat (definition)-able along with your other wealth.

If it was a partnership with a known profit margin, then the Mudarabah (definition) (profit-sharing) contract is invalid, and the entire profit belongs to you, while the worker is entitled to a wage equivalent to that of his peers (ujrat al-mithl). Zakat is obligatory on all the money, including its profit, upon the completion of a lunar year (hawl) from the moment the money came into your possession, and then you pay a quarter of a tenth (2.5%).