Answer
a) $y=-1000x+13000$
b) 9500 noodles
Work Step by Step
a)
3 dollars will sell 10000 noodles
5 dollars will sell 8000 noodles
$m=(10000-8000)/(3-5)$
$m=2000/-2$
$m=-1000$
$y=mx+b$
$y=-1000x+b$
$10000 = -1000*3+b$
$10000 = -3000+b$
$13000 = b$
$y=-1000x+13000$
b)
price is 3.50
$y=-1000x+13000$
$y=-1000*3.5+13000$
$y=-3500+13000$
$y=9500$