Answer
$I=44S-220$
Work Step by Step
The regression line is
$\qquad y=mx+b$,
where $m$ and $b$ are computed as follows.
$m=\displaystyle \frac{n(\sum xy)-(\sum x)(\sum y)}{n(\sum x^{2})-(\sum x)^{2}}\qquad b=\frac{\sum y-m(\sum x)}{n},$
$n=$ number of data points.
$\left[\begin{array}{lllll}
& S & I & SI & S^{2}\\
& & & & \\
\hline & 10 & 200 & 2000 & 100\\
& 15 & 500 & 7500 & 225\\
& 20 & 600 & 12,000 & 400\\
& 25 & 900 & 22,500 & 625\\
\hline & & & & \\
\sum & 70 & 2200 & 44,000 & 1350\\
& & & &
\end{array}\right]$
$m=\displaystyle \frac{4(44,000)-(70)(2200)}{4(1350)-(70)^{2}} =44$
$b=\displaystyle \frac{2200-44(70)}{4}=-220$
$I=44S-220$
