First step: We have changed x2 to x^2
Second step: 3x^2 x ^2 + 49
Third step: now lets factor out 9x^2 + 42 + 49
We have to list all of the factors but we will get to those later
Fourth step: you have to rewrite the polynomial by splitting the middle part term from using the 2 factors which was found in the factoring.
(9x^2 + 21x) + 21x + 41
Fifth step: We have to add up your first-two terms by pulling those factors we have been working with. 7(3x+ 7)
Sixth Step: try adding up the 4 terms. Thid id what I mean, ➡ 3x + 7 (3x + 7).
Seventh Step: we finally get your result for this equation
Answer: (3x +7)^2
From the looks of it option C. (3x + 7) (3x + 7) would be your answer
Good luck