If Nathan does 9 minutes of push ups for 3 days, that's 9 divided by 3, which is 3. (9/3=3) So nathan does 3 minutes of push ups each day, so just multiply each day by 3 to find the correlation between the two.
The Table should look like this:
# of days # of Minutes
1 3
2 6
3 9
4 12
5 15
6 18
7 21