The reason behind this is because if you think about it -7 is small number due to it being in the other side of the number line, and same goes with -5 and -1
For his total monthly bill to be under a twenty dollars he could make a 149 calls 20-5=15 15/.10=150 150-1=149 15-.10=14.9 14.9+5=19.9 So the maximum number of calls he can make is 149 a month
