Hey there! I'm happy to help!
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!
Have a wonderful day! :D