obs  y    x1   x2    x3
1  51.6  24.9  22  161.2
2  59.0  24.5  20  167.5
3  49.2  24.2  19  159.5
4  63.0  24.9  25  157.0
5  53.6  26.2  21  155.8
6  59.0  25.7  23  170.0
7  47.6  24.5  26  159.1
8  69.8  26.6  22  166.0
9  66.8  25.0  28  176.2
10 75.2  29.4  40  160.2
11 55.2  24.3  32  172.5
12 54.2  25.5  25  170.9
13 62.5  27.3  25  172.9
14 42.0  22.6  29  153.4
15 50.0  23.7  22  160.0
16 49.8  25.7  25  147.2
17 49.2  23.9  23  168.2
18 73.2  26.7  37  175.0
19 47.8  22.6  19  157.0
20 68.8  28.8  23  167.6