There are 24 boxes total. Pencils are $10 a box and erasers are $4 a box. Total cost is $210. What is the equation?

if you let p= # of pencil boxes and e= # of eraser boxes, then p + e = 24

if you a p # of pencil boxes at $10 per box and an e # of eraser boxes at $4 per box, then you will pay a total of $210:

($10)*(p) + ($4)*(e) = $210 ===> 10p + 4e = 210

system of equations to solve for p and e:

10p + 4e = 210

p + e = 24