If they drove a total of 5,300 miles in 2 days, and on the second day they drove 10 more miles then the 1st day.
5,300 ÷ 2 = 2,650
they drove 10 miles less on the first day
2,650 - 10 = 2,640
They drove 2,640 miles on the first day.
Hope this helps. :)