Answer:
In a week we have 7 days.
On the first day, Clare runs 4 miles.
On the other six days, she runs the same distance, let's call it D.
In total, she runs 22 miles.
Then:
4mi + 6*D = 22 mi
6*D = 22mi - 4mi = 18mi
D = 18mi/6 = 3mi.
Then the other 6 days, Clare runs 3 miles
Hope it helped! :)