Maths question really easy please help?

= x(x²+4x-1) - 3(x²+4x-1)

= x³ + 4x² - x -3x² - 12x + 3

= x³ + x² -13x + 3

(x-3)(x^2+4x-1)
So you can just turn it to be x(x^2+4x-1)-3(x^2+4x-1)
x(x^2+4x-1)=x(x^2)+x(4x)-x(1)
=x^3+4x^ 2-x
3(x^2+4x-1)=3(x^2)+3(4x)-3(1)
=3x^2+12x-3
and then,
(x^3+4x^2 -x)-(3x^2+12x-3)
=x^3+4x^ 2-x-3x^2-12x+3
=x^3-3x^2+4x^ 2-x-12x+3
=x^3+x^2+13x+3

this is not a convenient solution but i think it is more easy for you to understand,or you can just write
( x- 3 ) ( x^2 +4x -1 )
= x^3 + 4x^2 - x - 3x^2 - 12x + 3
= x^3 + x^2 - 13x +3

x^3 + 4x^2 - x
____-3x^2 - 12x + 3

X^3 + x^2 - 13x + 3

( x- 3 ) ( x^2 +4x -1 )
= x^3 + 4x^2 - x - 3x^2 - 12x + 3
= x^3 + x^2 - 13x +3

If x^2 means x squared then this is the answer.
X squared, 1x squared, -13x, 3
I use the method where you make a smiley face by drawing lines as you multiply your terms. Start at the left and multiply it by the first thing in the right hand brackets, then the second thing etc. then move to the second term in the left brackets and repeat.
Then collect like terms :)
My answer might not be righhtt...