little tip ... if it ends with a variable equaling a number, like x = 2 or y = 4, then there is 1 solution. if it ends with something unequal with no variable, like 0 = -4 or 5 = 7, then there is no solution. if it ends with something equaling with no variable, like 2 = 2 or 5 = 5, then there is infinite solutions.
6 servings = 3 people 1 cake=12 servings which feed 6 people 6/x=3/21 3x=126 x=42 servings 42 servings/12(amount of servings in a cake)=3.5. She will need to bake 4 cakes.