(x+4)(x-1)
First, find the factors of the constant (number without an x)
The factors of -4 are:
-1, 4
1, -4
2, -2
Looking at these factors find which pair of factors adds up to the middle number (3x)
4 + -1 = 3
Now you can factor this equation. Put x + 4 into one pair of parenthesis and x - 1 into another pair of parenthesis. You do this because you are separating the two factors into two expressions, that when multiplied together, will equal x^2 + 3x - 4
(x+4)(x-1) is the answer
To check this, multiply the two expressions together. You should get x^2+3x-4=0