algebra
posted by ken .
in 1991 the life expectancy of males in a certain country was 68.2 years. in 1995 it was 70.8 years. let e represent the life expectancy in year t and let t represent the number of years since 1991

look at it as two ordered pairs (0,68.2) and (4,70.8)
find the equation in the form
e = mt + b, just like you would find the equation of the line y = mx + b
since (0,68.2) is the yintercept
you already know
e = mt + 68.2
just find the slope m and you are done