I would say a triangle with two right angles because a triangle's angles add to 180 degrees. If a triangle has two right angles, it means that two angles will be 90 degrees, which add to 180 degrees. A triangle must have three angles and sides, and it is not possible for the last angle to be 0 degrees.
The equation you can use is x + 3x = 428 with x as the number of cheeseburgers and 3x the number of hamburgers you solve for x and get 4x= 428 and x=107
