how to simplify the following,please step by step

56x^7+21x^4+63x^3

first notice that each coefficient is a multiple of 7, so factor out the 7:

7(8x^7 + 3x^4 + 9x^3)

Now, note that all the powers of x are at least 3, so factor out the x^3:

7x^3 (8x^4 + 3x + 9)

I think that's as far as you can go here.