For (b), don't be distracted by the 600,000 megabytes. This is simply the maximum value of . The important figure is the 4000 megabytes that is needed, even if no pictures are stored.
In other words, if (where S is measured in megabytes.). This, then, is the intercept.
You're not quite correct in saying that the slope is . The slope is . So the formula you want is:Grandad