Hi!
<em>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:</em>
<em />
Now, when we plug it in the equation, it looks like this:

Therefore, your answer is 346.5 or, rounded, 347.
<em><u>Meaning, your answer is C</u></em>
<em><u></u></em>
Hope this helps and have a great day! :D