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13 miles in 13 minutes is easy.....  60 mph  

so he gets 50 MPG for 13 miles

 

1 24/60 x 68 = 95.2 miles @ 40 mpg

 

Gas used

13 m  /  50 m/gal = .26 gal

 

95.2 m  /  40 m/gal = 2.38 gals          total   2.64 gals