We see that Steve runs 2.5 miles per day and Sam runs 6.5 miles per day. If you add these together, we see that they run 9 miles every day.
We now need to see how many of these 9 mile days fit into this 450 miles. Let's divide 450 by 9 and we will see how many days it will take for them to reach 450 miles combined.
450÷9=50
Therefore, it will take Steve and Sam 50 days to reach 450 miles combined!