Well you can have a negative fraction as it means a downward sloping line. Truse me it's nothing to be perplexed over.
So lets use that slope intercept form:\(\displaystyle \L \;
y = \underbrace m_{slope}x + \underbrace b_{y - {\rm intercept}\)
Since the slope is the same, your new equation has the slope (\(\displaystyle m\)):\(\displaystyle \L \;\,-\,\frac{1}{3}\)
The y - intercept (\(\displaystyle b\)) is:\(\displaystyle \L \;1\)
So subsitute:
\(\displaystyle \L \;
y = \underbrace m_{slope}x + \underbrace b_{y - {\rm intercept}\)
\(\displaystyle \L \;y\,=\,\,-\,\frac{1}{3}x\,+\,1\)
In the future plz don't make duplicate threads. I hope you understand now.