You should explain whether a situation is linear or not. for instance, i have 2 scenarios below. which one is linear and how do you know?

situation a: my cell phone charges me $100 to register and then $0.10 per minute. how much will i be charged for 55 minutes?

situation b: bacteria double every day. if a bacteria culture has 5 organisms on the first day, how many bacteria will there be on day 10?