Kieran subscribes to a text messaging service on his cell phone. His monthly bill for the service is given by the equation b = 0.25t, where b is the bill amount and t is the number of texts. The constant of proportionality in terms of cost per text is ?
The question doesn't make a lot of sense, but I think the answer is $0.25, because In the equation b=0.25t, each text costs 25 cents
b=0.25t The cost of proportionality is 0.25