Carmen is a software saleswoman. her monthly salary is

$1800

plus an additional

$80

for every copy of math is fun she sells.
let
s
represent her total salary this month (in dollars), and let
n
represent the number of copies of math is fun she sells. write an equation relating
s
to
n
, and then graph your equation using the axes below.

we have three similar triangles, because each has a right angle and shares an angle.   let's write the angles in order: opposite to short leg, long leg, hypotenuse.

cab similar to bad similar to cbd

or as ratios,

ca: ab: cb = ba: ad: bd = cb: bd: cd

we also know

ac = ad + cd

(ad+cd): ab: cb = ba: ad: bd = cb: bd: cd

(ad+cd)/cb=cb/cd

we have cb=6, ad=5 and seek x=cd.

we reject the negative root and conclude x=4

answer: 4