Answer:
 26 minutes on the bicycle
Step-by-step explanation:
Let t and b represent the number of minutes on the treadmill and bicycle, respectively. The problem statement tells us two ways to relate these values.
 t + b = 60 . . . . . Amy exercises a total of 60 minutes (1 hour)
 9t +6.5b = 475 . . . . . she burns a total of 475 calories
Since we want to find the value of "b", we can use the first equation to write an expression that will substitute for t.
 t = 60 -b
 9(60 -b) +6.5b = 475
 540 -2.5b = 475 . . . . . . simpify
 -2.5b = -65 . . . . . . . . . . subtract 540
 b = 26 . . . . . . . . . . . . . . . divide by -2.5 (equivalently, multiply by -2/5)
Amy spends 26 minutes exercising on the bicycle.
