5a+(3x-3y-4a)
=5a+3x-3y-4a
=a+3x-3y
3x-(4y-2x+1)
=3x-4y+2x-1
=5x-4y-1
7a+3(a+3b)
=7a+3a+9b
=10a+9b
(x²-y²）-4(2x²-3y)
=x²-y²-8x²+12y
=-7x²-y²+12y