A garden shop wishes to prepare a supply of special fertilizer at a minimal cost by mixing two fertilizers, A and B. The mixture is to contain at least 45 units of phosphate at least 36 units of nitrate and at least 40 units of ammonium. Fertilizer A and B costs the shop $.97 per pound, $1.89 per pound respectively. Fertilizer A contains 5 units of phosphate, 2 units of nitrate and 2 units of ammonium. Fertilizer B contains 3 units of phosphate, 3 units of nitrate and 5 units of ammonium. How many pounds of each fertilizer should the shop use in order to minimize their cost?