By analyzing this graph we can see that it is a linear relation. Meaning that the Rate of Change is a consistent number, in this case $7. We know its $7 because by looking at the y coordinate for all present coordinates we can see a consistent difference of $7. From this point you could work backwards. Finding the coordinates for the first hour, which by doing $26 - $7 tells us the missing number for the first coordinate pair (1,19). Then we work backwards one more time, this time subtracting $7 from $19, and this tells us the initial value (the coordinate on the y-axis), which is $12. One thing you can do to show your work is draw a straight line that intersects all the coordinates and the y-axis, the line should intersect the y-axis at these coordinates (0,12). Now I could be wrong but if there is a formula that is used to determine this answer then I am unaware of it. Hope this helps however
