Question 175365
The average lifespan of American women has been tracked, and the model for the data is y = 0.2t + 73, where t = 0 corresponds to 1960. 

What is the slope? It is m = 0.2. This values tells me that, for every increase of 1 in my input variable t (that is, for every increase of one year), the value of my output variable y will increase by 0.2.
 
What is the meaning of the slope? It means that, every year, the average lifespan of American women increased by 0.2 years, or about 2.4 months.

When t = 0, what is the value of y? Looking at the equation, I see that  y = 73.

What is the meaning of this y-value? It means that, in 1960 (when they started counting), the average lifespan of an American woman was 73 years.