First we must assume the relationship of the number of chirps and temperature. SO assuming that they are directly proportional, therefore the equation is:
T = k C
where T is temperature, k is proportionality constant, and C is number of chirps
So at T = 50 degrees, C = 40 / min, k is:
50 = k * 40
k = 1.25
So the equation relating the two is:
T = 1.25 C