Question 518399
Let 
He Drove at 40mph = t hours
He Drove at 58mph = 13-t hours
Distance he covered at 40mph = 40t
Distance he covered at 50mph = 50(13-t) 
Total Distance covered = 646


Distance he covered at 40mph  + Distance he covered at 50mph = Total Distance covered
40t+50(13-t)=646
40t+650-50t=646
40t-50t=646-650
-10t=-4
-10t/t=-4/-10
t=4/10
t=2/5 

He Drove at 40mph = t = 2/5 hours or 24 minutes
He Drove at 58mph = 13-t = 13-(2/5)=(65-2)/5=63/5= 5hours 3/5 minutes (36 minutes)

Check
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Distance he covered at 40mph = 40t = 40 * 2/5 = 8*2=16 miles
Distance he covered at 50mph = 50 * 63/5 = 10*63=630 miles
Sum both distances = 16+630=646 miles