Answer:
Super Mario Land is a fairly common Gameboy game so it's not worth much unless it is new/unboxed or unless it is in very good condition with all its paper work ( ads, offers, instruction booklet)
Gamestop: too old to sell it there they wont accept it
Pawn shop: 0.50-3.00$
since Mario land is a farily common game even if it is unboxed mint condition or new it still probably wont be worth what you paid for it
the most you can sell it for at a yard sale is 10$
the most reasonable price would be 7$