Answer:
(The problem doesn't have solution as stated, i think you press 5 instead of $ on 535 and 50.16. With this as initial prices, they would never cost the same.)
Step-by-step explanation:
We can express the charge <em>c</em> of the Call First company as:
where <em>m</em> is the number of messages sent.
For Cellular plus
.
Now, for a number of messages m' the cost will be the same
Now, we can work the equation a little
So the number of messages that needs to be sent have make both plans cost the same is 125.