Answer
60 chirps per minute
Work Step by Step
Using the formula T = 50 + $\frac{N - 40}{4}$, substitute the value given into the equation.
55 = 50 + $\frac{N - 40}{4}$
Solve for N:
5 = $\frac{N - 40}{4}$
20 = N - 40
60 = N
Interpret: 60 chirps per minute