On Chatty Cathy’s cell phone plan she pays for minutes used plus a fixed monthly charge. For 500 minutes she pays $35 total, and for 1500 minutes used she pays $55 total.

Question

What is her monthly fixed charge?

A) $15
B) $20
C) $25
D) $30

Answer 1

y = mx+b, so

500m+b = 35
1500m+b = 55

so,
1500m+3b = 105
1500m+b = 55

2b = 50
b = 25