Question 1025405
50 is the fixed cost. This is what you pay no matter how many months you use it for. This is the sign up fee. 


15 is the variable cost. This is attached to the variable x because 15x means 15 times x. This helps determine how much you pay in total if you ignore the fixed cost


Combining the two gives 15x + 50 which is the total cost. So that's why the answer is choice A