4. In his Ph.D. thesis, H. Behbahani examined the effect of varying the wa- ter/cement ratio on the strength of concrete that had been aged 28 days. For concrete with a cement content of 200 pounds per cubic yard, he obtained the data presented in the following table. Let Y denote the strength and r denote the water/cement ratio. Water/Cement Ratio Strength (100fulb) 1.21 1.302 1.29 1.231 1.37 1.061 1.46 1.040 1.62 0.803 .79 0.711 (a) (6 pts) Find the equation of the least squares line y = a | Br. ( You can use _ riyi = 8.709, Cri = 8.74 and _ yi = 6.148. )