Question

Using the sieve of Eratosthenes, circle the number two, now cross out every multiple of two and write an algebraic expression for the numbers u crossed out

Answer 1

there isnt really a question here, but what you've written does seem to be the seive of Erato.. if I remember it correctly. just follow the directions and im sure you'll be fine.

Answer 2

i suppose, it is asking a question, to write an expression for all the even numbers (as that is the 1st set of crossed out numbers, and all multiples of 2 are all the evens)
n=2k
would be that relation.
ex:
2*1=2
2*2=4
2*3=6
...
2*(n-1)=2n-2
2n=2n