#### Answer

$y=7.2t+11.9$

#### Work Step by Step

Graphing the approximately linear function,
the points on the graph are (t, y(t)).
Let y be in billions of dollars,
t is the number of years after 2000.
Given points: (1, 19.1) and (8, 69.7).
Slope:
$ m=\displaystyle \frac{69.7-19.1}{8-1}=\frac{50.6}{7}\approx$7.22857142857$\approx 7.2$
Point-slope equation:
$y-19.1=7.2(t-1)$
$y-19.1=7.2t-7.2\qquad/+19.1$
$y=7.2t+11.9$