1)15a+10b-5ab-30=5(3a+2b-ab-6)=5( a(3-b) + 2(b-3) ) =5( a(3-b) - 2(3-b) ) =5(a-2)(3-b) 

2)75+15n-12mn-60m=3(25+5n-4mn-20m)=3( 5(5-4m) + n(5-4m) ) = 3(5-4m)(5+n)

3)-30k+30-10p+10kp=10(-3(k-1) + p (k-1) )=10(p-3)(k-1)

4)12x^2+12y-16x-9xy=4x(3x-4)+3y(4-3x)=4x(3x-4)-3y(3x-4)=(3x-4)(4x-3y)