your code
mothership(500,500);
shuttle(50,100,5000);
fuel(500,200,3500);
planet(50,500,"venus");
wall(100,100,600,100);
wall(100,100,100,500);
planet(500,50,"mars");
fuel(350,300,3000);
planet(300,460,"mercury");
alien(150,200,450,200);
fuel(50,200,2000);
wall(450,200,450,650);
planet(350,150,"earth");
alien(150,150,150,400);
wall(100,200,300,200);