Answer: here are 3: 42/112, 63/168 and 84/224
Step-by-step explanation:
42/112 (because 21 * 2 = 42 and 56 * 2 = 112)
63/168 (because 21 * 3 = 63 and 56 * 3 = 168)
84/224 (because 21 * 4 = 84 and 56 * 4 = 224)
