y=3(x+1)(x-5)
I'm going to ignore 3 for now, but will add it later.
FOIL the (x+1)(x-5)
F = multiply the First numbers x and x
O = multiply the Outside numbers x and -5
I = multiply the Inside number 1 and x
L = multiply the Last numbers 1 and -5
3(x^2 + -5x + 1x + -5)
add -5x and x
3(x^2 + -4x + -5)
multiply the numbers inside the parenthesis by 3
3x^2 + -12x + -15
