a)(2x-3) (4x+1)=8x^2+2x-12x-3=8x^2-10x-3

b)(3x-y)(2y-7x)=6xy-21x^2-2y^2+7xy=-21x^2+13xy-2y^2

c)a(a+4)-(a-2)(a+6)=a^2+4a-(a^2+6a-2a-12)=12

d)(1-3b) (9b^2+3b+1)=9b^2+3b+1-27b^3-9b^2-3b=1-27x^3