Given:
Greg drives north 7.4 miles and stops at the store.
Then he drives 5.7 miles south to his friend's house.
To find:
The shortest distance between Greg's house and his friend's house.
Solution:
Greg drives north 7.4 miles.
He drives 5.7 miles south.
The shortest distance between Greg's house and his friend's house is difference between distance he drives north and distance he drives south.
Shortest distance = (7.4 - 5.7) miles
= 1.7 miles
The shortest distance between Greg's house and his friend's house is 1.7 miles.
Therefore, the correct option is C.