This question is really straight forward
By using the Chain rule: f'(x) = uv' + u'v.
let u=3x, so u'=3
let v=(2x-1)^2, so v'=2x2(2x-1)=8x-4
Now, we put this expression altogether:
As f'(x) = uv' + u'v
f'(x)=3x(8x-4)+3(2x-1)^2
f'(x)=24x^2-12x+12x^2+3-12x
And now, simplify
f'(x)=36x^2-24x+3