探索计算：弹簧挂上物体后会伸长．已知一弹簧的长度（）与所挂物体的质量（）之间的关系如下表：                                                                                                                                                                    

所挂物体的质量	0	1	2	3	4	5	6	7
弹簧的长度	12	12.5	13	13.5	14	14.5	15	15.5