size of herd = 0-50 with value output per £ 100 on input is 75; size of herd = 51-75 with value output per £ 100 on input is 89; size of herd = 76-100 with value output per £ 100 on input is 91; size of herd = 101-150 with value output per £ 100 on input is 99; size of herd = 151-200 with value output per £ 100 on input is 109; size of herd = 201-300 with value output per £ 100 on input is 105; size of herd = 301+ with value output per£ 100 on input is 111. What size of dairy herd is most efficient?