Answer: The family need to drive 2664.8 miles to reach Anchorage.
Explanation:
Given : Total distance from San Antonio, Texas, to Anchorage, Alaska = 4304 miles
They have already driven 1639.2 miles.
Then, the distance needs to be travel to reach Anchorage = 4304- 1639.2 miles
=2664.8 miles
Hence, the family need to drive 2664.8 miles to reach Anchorage.