We have that last most the bill was over $90, if the initial cost is $70 for 500 min
[tex]90-70=20[/tex]
If the cost for an additional minute is $0.40
[tex]0.40m>20[/tex][tex]m>50[/tex]
More than 50 additional minutes were used
ANSWER
C. More than 50 additional minutes were used
