Hi there, AirConditioning,
The equation we will be using is linear, and takes the form y = slope*x+b, where slope is equivalent to the fireflies caught each minute.
y=total fireflies caught
You : y = 3m+13
Your Friend: ym+6
Fireflies caught each minute
You: 3
Your Friend: 4
3+4=7
A total of 7 fireflies each minute combined.