Parameterize the lateral face

of the cylinder by

where

and

, and parameterize the disks

as


where

and

.
The integral along the surface of the cylinder (with outward/positive orientation) is then




The slope of her function represents the amount she earns per door that she knocks on.
Y=mx+b is the slope formula
Answer: the maximum number of drinks Liam can buy is 4 without over exceeding his price limit.
work:
$3.50 for 5 tacos is $17.50
9 - 5 tacos = 4 drinks
4 drinks x $2 = $8
$17.50 + $8 = $25.50 out of $30 price limit
Divide by 100. 350/100=3.5 which is 3 and 1/2