Take two points and find the slope. (4,9) (6,13) y2-y1/x2-x1 4/2=2=m y=2x+b 9=8+1 b+1 y=2x+1 Set x to 10 to find the 10th week y=20+1 21 miles Set y=26.3 to find which week. 26.3=2x+1 2x=25.3 x=12.6 weeks or round to 13 weeks I think he should round up because in more slopes in between points, there is a lesser slope than 2. Hope this helps.
One way is to type it into your trusty TI and use the table from presing stat and then stat againg then calc then 4 so the equation that I got from your set of points is y=1.983333333333333x+0.80555555555
