## Thinking Mathematically (6th Edition)

Fill the blank with $4.00+0.15x$
The monthly cost consists of two parts: * the cost based on the number of messages, ** the fixed cost, regardless of the number of messages. The sum of the two is the total cost. So, total monthly cost equals (number of messages)$\times$(cost of one)+ (fixed cost) which we write as $x\cdot 0.15+4.00$ or $4.00+0.15x$ Fill the blank with $4.00+0.15x$