Hi!
To calculate the rate of change between days 4 and 6, we simply take those points, (4, 1503) and (6, 2196) and use the equation in the picture below:
Now, when we plug it in the equation, it looks like this:
[tex]\frac{2196-1503}{6-4} = \frac{693}{2} = 346.5[/tex]
Therefore, your answer is 346.5 or, rounded, 347.
Meaning, your answer is C
Hope this helps and have a great day! :D