Show that

(x + 1)(x – 3)(x – 4) = x3 – 6x2 + 5x + 12

I'm so sorry but I can't show any working for this as I don't have a clue how to factorise when there are no common letters and numbers? Thanks!

It's already factored! You need to review how to multiply polynomials

It all hinges on the distributive property.

(x+1)(x-3) = x(x-3)+1(x-3)
= x^2-3x + x-3
= x^2-2x-3

Now multiply that by (x-4) and you have

(x^2-2x-3)(x-4)
= x^2(x-4)-2x(x-4)-3(x-4)
= x^3-4x^2-2x^2+8x-3x+12
= x^3-6x^2+5x+12