A)
Cost y= 1/2x + 40
Revenue y= 3x
Brake even point (20,60)
The cost is how much he pays for a number of stickers each sticker cost him 50¢ plus a $40 fee probably for shipping
The revenue is how much he sells them for $3 a sticker
The break even point is when he has made his money back
B)
The slope would be smaller which would cause him to have to sell more stickers to break even
C)
If I'm right and the 40 fee is shipping my advise would to be to buy in bulk