Answer
$y=0.7x+0.85$
Work Step by Step
Regression line $y=mx+b,$ 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.
The quantities $m$ and $b$ are called the regression coefficients.
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Build a table
\begin{array}{|cc|c|c|c|cc|}
\hline & x & y & xy & xx \\
\hline & 0 & -1 & 0 & 0 \\
& 1 & 3 & 3 & 1 \\
& 3 & 6 & 18 & 9 \\
& 4 & 1 & 4 & 16 \\\hline
\Sigma & {\bf 8} & {\bf 9} & {\bf 25} & {\bf 26} \\\hline
points & 4 & & 100 & 104 \\\hline
\end{array}
$m=\displaystyle \frac{n(\sum xy)-(\sum x)(\sum y)}{n(\sum x^{2})-(\sum x)^{2}}=\frac{100-(8)(9)}{104-(8)^{2}}=\frac{28}{40}=0.7$
$b=\displaystyle \frac{\sum y-m(\sum x)}{n}=\frac{9-0.7(8)}{4}=0.85$
$y=0.7x+0.85$
