I'm supposed to identify vertical intercept and slope and explain meanings in practical terms. I understand what vertical intercept is , and I know how to get slope, but I am confused when it's in a word problem like below:

1. The population of a town can be represented by the formula P(t) = 54.25 - 2/7t, where P(t) represents the population, in thousands and t represents the time in years, since 1970. (Does this mean that P(t) is y and 2/7 is my slope?)

2. The profit, in dollars of selling n items is given by P(n)=0.98n-3000.

(does this mean that .98 is the slope, -3000 is y-intercept? but what is vertical intercept -- do I have to put it into another equation - or solve by putting in values for n?)

3. A phone company charges according to the formula C(n)=29.99 +0.05n, where n is the number of minutes, and C(n) is the monthly phone charge, in dollars

still don't understand vertical intercept -- I think the .05 is the slope though