Question 903271
a+b=4,
60*a+74*b=275
a=4-b
60*(4-b)+74*b=275
240-60b+74*b=275
14*b=35
b=2.5 
a=4-b
a=1.5 hours at 60 mph  and  b=2.5 hours at 74 mph
check
1.5+2.5=4
60*a+74*b=275
60*1.5+74*2.5=275
90.0+185.0=275
275.0=275
ok