Question

Using the line of best fit, estimate how may miles Jack ran the 10th week; show work.

Answer 1

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.

Answer 2

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