Answer:
60 minutes including the 15 minute rest.
Step-by-step explanation:
450/10 is 45. Therefore, biking for 45 minutes will loose 450 calories, 10 calories per minute. Maybe half way during the 45 minutes Spencer will take the 15 minute rest. This brings the biking trip 60 minutes.
Answer:

Step-by-step explanation:

Using this, we can subtract and find the answer.

Answer:
C)infinitely many solutions
Step-by-step explanation:

One could be |x|<-2
This could be one since no matter what you put in for x, it will always be positive.