nitrogen	animal	body-wt
15.8	1	30
21.3	1	60
16.5	1	90
16.4	2	30
20.8	2	60
18.2	2	90
17.3	3	30
23.8	3	60
17.8	3	90
16.4	4	30
22.1	4	60
17.5	4	90