Answer:
he would of traveled 420 km by the seventh day.
Step-by-step explanation:
you get this by adding all the numbers together like this
      15 + 30 + 45 + 60 + 75 + 90 + 105 = 420 km
days/ Â Â 1 Â Â Â 2 Â Â Â 3 Â Â Â 4 Â Â Â 5 Â Â Â 6 Â Â Â 7 Â / total distence