A calculator can be used, provided it is "wide" enough -- the display can handle 10-digit numbers. The answer might be displayed in scientific notation, which is a great thing to learn about if you don't already know!
"Shortcut": the first number ends in 9 zeros; the second number ends in 9 zeros. 3 times 9 is 27. The answer will begin with 27 and end with 9 + 9 zeros.
27000000000000000000
27,000,000,000,000,000,000
Twenty-seven quintillion!