You're right so far, but you need the prime factorization. You should end up with the same radicand, so they can be added.
Let me complete the first one for you, so you can see how it's done:
We have √63 + √175 + √112
√63 = √3 X 3 X 7. There's a pair of 3's and a 7 left over, so pull out the 3 to make 3√7
√175 = √5 X 5 X 7. There's a pair of 5's and a 7 left over, so pull out the 5. 5√7
√112 = √2 X 2 X 2 X 2 X 7. We have 2 pairs of 2's, so that becomes 4. 4√7
3 + 5 + 4 = 12. So the final answer is 12√7
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