y=9-x is slope-intercept form of that line, which means it has a slope of -1. Parallel lines have the same slope, so the slope of this new line will also be -1.
To find the line that goes through (5,1), we can use a blank equation y=mx+b. We know that m=-1, so we can use the given point to find b:
y=mx+b
Y=-x+b
1=-5+b
6=b
So the line would be y=-x+6.
