Solve in cost function. Pmobile charges $30 for the first 300 minutes and 50 cents for each additional minute.

Question

the answer is some thing like this p(m)=30 if m < 300.

Answer 1

You have the first part right, if m < 300 the charge is 30.  

 

If m >= 300 the charge is 30 plus 0.50 for each minute above 300, which is 

 

p(m) = 30 + 0.5*(m-300)  if m >= 300

 

You can simplify this to p(m) = 0.5*m - 120  if m >= 300