How do you find the greatest common factor of 18 and 54 using the sieve of eratosthenes?

By finding all the factors of the numbers and see which one is the biggest # they have in common. Or look at the Sieve of Eratosthenes table at google.com and there you will find the answer.
or by looking at a sieve of Eratosthenes and crossing out the factors of each number and seeing which two factors are the same but the highest out of them both.