Oliver buys yen stamps each costing 77cents

complete the calculation he could do to find the total cost

Hi!

I think that you misspelled the question, and you mean that Oliver bought "ten", not "yen" stamps - yen is the currency of Japan.

So we have 10 stamps of 77 cents each:

10*77=770 cents

He has to pay 770 cents, or since 100 cents are one dollar, 7 dollars and 70 cents.