Answer:
The answer is B because x = 4 so 12x4-3=45
27.7-14=Cost above 500 msg
13.7=C
E=number of Extra messages sent
C=0.1E
13.7/0.1=E
137=E
Total messages=T
T=500+E
T=500+137
T=637
Danielle sent 637 messages in September