It is believed that a certain drug can reduce a patient's pulse rate. In an experiment it was found that the larger the dose of the drug, the more the pulse rate reduced. A doctor wishes to find a regression equation which could be used to predict the pulse rate achieved for specific dosages. An experiment is carried out on four healthy individuals, varying the dose, $x($in $g),$ and measuring the corresponding pulse rate, $y($in beats per minute$).$ The table below shows values of $x$ and $y$ measured on $4$ students.

$\backslash$table$[[$Individual$,$Dose $x_i,$Pulse rate $y_i$