Answer: 231,469.335
Step-by-step explanation:
Technically, none of the equations.
The equation you're looking for would be:
x²+(x+20)²=150²
Time used for the call to Zurich: ($5-$1.25)/$0.25=15 minutes
15minutes+3minutes=18minutes
Time used for the call to London: ($7.25-$1.25)/$0.25=24 minutes
24minutes+3minutes=27minutes
Difference between the two calls:27-18=9minutes
