Answer:
(a) 12x + 6y = 120
(b)

(c)

Explanation:
Andrew needs exactly 120 pencils.
The supply closet have boxes of pencils with 12 in each and boxes of markers with 6 in each .
Let x be the number of pencil boxes
and y be the number of marker boxes
12(pencil boxes) + 6(marker boxes) = 120
So equation becomes
12x + 6y = 120
(b)Now solve the equation for x
12x + 6y = 120
Subtract 6y on both sides
12x = 120 - 6y
Divide both sides by 12


(c)Now solve the equation for x
12x + 6y = 120
Subtract 12x on both sides
6y = 120 - 12x
Divide both sides by 6

