Answer:
175 miles
Explanation:
Hillary has travelled
320 + 350 = 670 miles
in the first two weeks.
Therefore, Hillary starts with 670 miles and needs to add a certain number of miles "x" to get 845 in total.
670 + x = 845
And if we subtract 670 from both sides:
x = 845 - 670 = 175
175 miles