Idont know what to do to get my answer

Closing a credit card usually _your debt ratio.a. increasesb. decreasesc. improvesd. has no effect on

Math i have no idea how to do a and b

One cell phone plan charges $20 per month plus $0.15 per minute used. a second cell phone plan charges $35 per month plus $0.10 per minute used. write and solve an equation to find the number of minutes you must talk to have the same cost for both calling plans.