Answer:

| $X$ | $y$ | $X-3.5$ | $2\times\big(X-3.5\big)=x$ | $xy$ | $x^2$ | | --- | --- | --- | --- | --- | --- | | 1 | 49 | -2.5 | -5 | -245 | 25 | | 2 | 54 | -1.5 | -3 | -162 | 9 | | 3 | 60 | -0.5 | -1 | -60 | 1 | | 4 | 73 | 0.5 | 1 | 73 | 1 | | 5 | 80 | 1.5 | 3 | 240 | 9 | | 6 | 86 | 2.5 | 5 | 430 | 25 | | N=6 | 402 | | 0 | 276 | 70 |   $\Sigma \ y=N\times a+b\times\Sigma \ x $ $402=6\times a+b\times (0)$ $a=\dfrac{402}{6} = 67$ $\Sigma \ xy= a\times \Sigma\ x+b \times \Sigma \ x^2$ $276=a \times (0)+b\times 70$ $b=\dfrac{276}{70} = 3.9429$ ∴ The equation of the line is $y=a+ b\times x= 67 + 3.9429\ x.$   Resubstituting the value $y=Y and \ x=2\times \big(X-3.5 \big)$,   ***The equation of the line now is:*** $Y= 67+ 2\times \big(X-3.5\big)\times \ 3.9429$ **$Y=39.3997+ 7.88X $**