A dietician wishes to mix two type of foods in such a way that vitamin contents of the mixture contain at least 8 units of vitamin A and the 10 units of vitamin C. Food I contains 2`(unit)/(kg) ` of vitamin A and 1`(unit)/(kg)` of vitamin C. Food II contains 1 `(unit)/(kg)` of vitamin A and 2`(unit)/(kg)` of vitamin C. It costs Rs.`(50)/(kg)` to purchase food I and Rs. `(70)/(kg)` to purchase food II. Formulate this problem as a linear programming problem to minimise the cost of such a mixture ?