Is the additional sum of 50.0 DZD considered usury, or is it permissible in Islamic law for the construction project in which I participated with money only, on the condition that I receive 200.0 DZD in return for 150.0 DZD?

This partnership is invalid for two reasons: First, guaranteeing the capital of the partnership, which is impermissible because the two partners share in profit and loss together, and the condition of guarantee in qirad (commenda) is void. Second, specifying a fixed amount in this partnership invalidates it. What is obligatory is for the profit to be a shared part, such as half or a quarter. These two conditions invalidate the partnership, and it must be corrected by nullifying them. For what has passed of it, the profit belongs to the owner of the capital, and the mudarib (working partner) receives the wage of the like.