here is a variation of your question.
http://www.jiskha.com/display.cgi?id=1294619397
As you can see in the "related questions" below, this seems to be a popular type of question.
In 1992, the life expectancy of males in a certain country was 63.8 years. In 1999, it was 66.0 years. Let E represent the life expectancy in year t and let t represent the number of years since 1992. The lineahntthe nearest ter function E(t) that fits the date is? Use the function to predict the life expectancy of males in 2004. round both to
3 answers
E = m y + b
y is year - 1992
63.8 = m(0) + b
b = 63.8
so
E = m y + 63.8
66.0 = m (1999-1992) + 63.8
2.2 = m (7)
m = .3143
so
E = .3143 y + 63.8
or
E = .3143(year-1992) + 63.8
part b:
in 2004 y = 2004-1992 = 12
E = .3143(12) + 63.8
= 67.6
y is year - 1992
63.8 = m(0) + b
b = 63.8
so
E = m y + 63.8
66.0 = m (1999-1992) + 63.8
2.2 = m (7)
m = .3143
so
E = .3143 y + 63.8
or
E = .3143(year-1992) + 63.8
part b:
in 2004 y = 2004-1992 = 12
E = .3143(12) + 63.8
= 67.6
Looks like I did it faster back then :)