tolong dijawab no. 15-18!!please kasih tau cara penyelesaiannya!

15.L=p xl
       =(5x -2)(4x -7)
       =20x²-35x-8x-14
       =20x²-43x-14...........b
16.(3a-4b)(3a-4b)
   =9a²-12ab-12ab+16b²
   =9a²-24ab+16b²...........d
17.3(x-1/x)(x-1/x)
    =3(x²-1-1+1/x²)
    =3(x²-2+1/x²)
    =3x²-6+3/x²...................c
18.(3b-2)(3b-2)-(b-3)(b-3)
   =(9b²-6b-6b+4)-(b²-3b-3b+9)
   =(9b²-12b+4)-(b²-9b+9)
   =9b²-12b+4-b²+9b-9
   =8b²-6b-5...........................b