For 17 put the two points in a x y chart and find the slope.
x y
0 5
9 4
the difference between 0 and 9 is 9. the difference between 5 and 4 is -1. so the slope is -1/9. the y-intercept is given to you in one of the points. so, the equation of the line would be y= -1/9x + 5.
Number 18 is the same, its just sneakily giving you the second point.
x y
0 -8
3 10
the difference between 0 and 3 is 3. the difference between -8 and 10 is 18. so the slope is 18/3, which and be simplified to 6/1 aka 6. since it already tells you the y-intercept, no math needs to be done :). the equation of the line would be y= 6x - 8. i hope this helps!!! good luck