49x^2 + 42xy + 9y^2 factor completely.

49x^2+42xy+9y^2

To factor a quadratic of the form ax^2+bx+c, you must find two values, j and k, which satisfy two conditions:

jk=ac=441 and j+k=42, so j and k must be 21 and 21.

Now replace bx with jx and kx in the original equation.

49x^2+21xy+21xy+9y^2  now factor 1st and 2nd pair of terms...

7x(7x+3y)+3y(7x+3y)  which is equal to

(7x+3y)(7x+3y)  which is equal to

(7x+3y)^2

Ithink the answer is b i hope it my friend message me if i’m wrong and i’ll change my answer and fix it for you