Syd and David decided to travel from California to Maine in Syd’s 1942 Cadillac. They allowed 10 days to make the trip. On Wednesday and Thursday, Syd and David drove 750 miles over a 15 hour period. What was the average speed hour at which they drove on these two days? A- 25mph
B- 50mph
C- 55mph
D- Not here

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let x and 400 - x be the two numbers.  

==> 0.80x + 0.85(400 - x) = 400 - 68 from the statement of the problem.  

< ==> 0.80x + 0.85(400 - x) = 400 - 68  

==> 340 - 0.05x = 332  

< ==> -0.05x = -8 ==> x = 160, the first number ==> 400 - x = 240, the second number.