In all likelihood y5t trend is stationery as can be seen from the above trend.
The null hypothesis:
H0: B1 = B2 = B3 = 0
Ha: At lease one B is non-zero.
It is clear from the above test that the null hypothesis exists here with y5 and y1 moving tandem with each other. The graph below further helps in understanding the movement in y5 and y1.
