What is the amount of zakat due in cash on two plots of land that were purchased with the intention of selling, the first being sold after 5 years with a profit, and the second after 4 years also with a profit, bearing in mind that the buyer was unaware of the obligation of zakat on them, and that the zakat threshold is estimated at 85,0 dinars?

Zakat (definition) is not obligatory on land unless three conditions are met: it was purchased with the intention of trade, its value reaches the nisab (definition) by itself or when combined with other assets, and a full year (hawl) has passed on the money used to purchase it, or on the land itself if its value was less than the nisab. If these conditions are met, zakat becomes due annually, which is a quarter of a tenth (2.5%) of its estimated value each year.