Factorise

a) x + 3x - 4

(x-1) (x+4)

Step-by-step explanation:

I'm guessing you meant x^2+3x-4.

The easiest part is knowing that:

(x-_) (x+_)

You have to look for numbers that multiply to - 4 and add up to 3. Therefore, it would be - 1 and 4:

(x-1) (x+4)

The answer to this equation is 4 (x-1)