A and B can do a piece of work in 10 days B and C can do it in 15 days a and c can do it in 20 days how long will they take to do it individually​

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.