she needs to earn at least 84 to buy the mp3 player
earnings=earningsperhour times numberofhoursworked
earnings per hour=12 dollars
number of hoursworked=h
therefor
earnings=12 ties h or12h
earnings is at least 84
earnings is greater than or equal to 84
earnings>84
12h>84
solve
12h>84
divide both sides by 12
h>7
she needs to work at least 7 hours
to graph, draw a line at x=0 and shade to the right, make the line solid