We will need to check for each week
y = 3.25x + 8.5
week 1
substitute x = 1 in the above
y = 3.25(1) + 8.5 = 3.25 + 8.5 = 11.75
11.75 is less than 13
week 2
substitute x= 2 into the equation
y = 3.25(2) + 8.5 = 6.5 + 8.5 = 15
15 is less than 15.5
week 3
substitute x=3 into the equation
y = 3.25(3) + 8.5 = 9.75 + 8.5 = 18.25
18.25 is greater than 15.5
week 4
substitute x=4 into the equation
y =3.25(4) + 8.5 = 13 + 8.5 = 21.5
21.5 is less than 22.5
week 5
substitute x = 5 into the equation
y = 3.25(5) + 8.5 = 16.25 + 8.5=24.75
This is greater than 23
week6
substitute x=6 into the equation
y = 3.25 (6) + 8.5 = 19.5 + 8.5 =28
28 is less than 30
Hence in week 3 and week 5, the number of miles given by the equation is greater than the actual number of miles the athlete will run.