First, find the slope. You got two points: (0, 70.7) and (6, 74.6). The x-coordinates are years since 1993, and the y-coordinates are the life expectancies.
Second, you need the y-intercept. Oh, wait, one of the points is the y-intercept, so b = 70.7.
You have the two pieces of information needed to write the function:
E(t) = 0.65t + 70.7