If it take some x minutes to upload some y digital photographs, it means it has an average of: x/y minutes to upload a single digital photograph. Then, to upload z photographs, you just multiply x/y by z.
Spoilers for answer:
If it take 7.2 minutes to upload 8 digital photographs, it means it has an average of: 7.2/8 = 0.9 minutes to upload a single digital photograph. This means that, by this rate, it will take 20 * 0.9 = 18 minutes to upload 20 photographs to the website.
Erik will pay $18.75 for the cashews.
58 plus tip of .20
so
58 times 0.2 = 11.6 is the tip
now we add tax (Presuming we son't tax the tip)
58 times 0.07 = 4.06 the tax
so its
58 + 11.6 + 4.06 = $73.66 total cost
I think its the last one, Aidan can expect to save about $27.52 each week. Hope I was correct