Question 169710
lets call the cost of mp3 player m and the cost of headphones h
:
5m+8h=840....eq 1
3m+4h=480....eq 2
:
you now have (2) a system of linear equations 
:
solving we have {{{highlight(m=120)}}}dollars a piece for mp3 players 
................{{{highlight(h=30)}}}dollars a piece for headphones
:
*[invoke linear "m", "h", 5, 8, 840, 3, 4, 480]