Answer
a) $y=90000x+83000$
b) estimated 533000 vehicles
Work Step by Step
a)
2004 had 83000 vehicles
2007 had 353000 vehicles
$2004-2004 = 0$
$2007-2004 = 3$
$(0,83000)$ and $(3,353000)$
$m=(353000-83000)/(3-0)$
$m=270000/3$
$m=90000$
$y=mx+b$
$y=90000*x+b$
$353000=90000*3+b$
$353000 = 270000+b$
$83000 = b$
$y=90000x+83000$
b)
$y=90000x+83000$
In 2009,
$2009-2004=5$
$y=90000x+83000$
$y=90000*5+83000$
$y=450000 + 83000$
$y=533000$