What you need to do is multiply the number which is in front of the ( & ) with that what is in it, -12y(y-6):
Multiply y with -12y, that's -12y^2. muliply -6 with -12y that's 72y (negatif x negatif is positif), so -12y^2 + 72y and than futher as has been shown in the past answers