a) Three partners, Amani, John and Mary, operate groceries in the same locality. On a particular day they compared their sales proceeds and found that the prices at which one bought an item is the same at which another would sell the same item. If Amani purchased 4 units of Onions and sold 3 units of Tomatoes and 5 units of Potatoes. Mary purchased 3 units of Potatoes and sold 2 units of Tomatoes and 1 unit of Onions. John purchased 1 unit of Tomatoes and sold 4 units of Potatoes and 6 units of Onions. In the process. Amani, Mary and John earn Ksh 6,000/-, Ksh 5, 000/- and Ksh 13, 000/- respectively, from these transactions. Required: i. Form systems of linear equations and the prices per unit of the three categories