Answer:
S = 20 + 0.5*x (S is the total bill, x is the number of text messages)
Step-by-step explanation:
The cell phone company have a fixed value you have to pay every month, independently of the number of text messages you send, and that is $20.
For each text message, you pay an additional %0.50.
So, if you send 'x' text messages in a month, you will pay the fixed $20 plus $0.5 for each text messages: you will pay 0.5 times x for the messages.
So, we can formulate the following equation:
Being "S" the total price you will pay:
S = 20 + 0.5*x
