(I cannot be the number line bit sorry)
When you're finding which one is greater, you can either write these out in words, or you can put them next to eachother.
In words- Olivia: Two million, three hundred and six thousand, four hundred and twenty one. (2306421)
Clayton- Two million, three hundred and two thousand, nine hundred and seventy two. (2302972)
From writing them out, you can see that Olivia's score has 'three hundred and six thousands', where as, Clayton has 'three hundred and two thousand'
Therefore, Olivia got the higher score.
Hope this helps :)