F(x) = -2/3 | x + 4 | + 3/x - 4 + 5x^2; f(-2/3) I already know the answer is -9/14, but I need to know how to get there

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.