a-(a-(a-4))
7x*((y-x)+3y)
4y-(3y+(2y(y+1)))
5c-(2c-((b-c)-2b))

a-(a-(a-4))=a-(a-a+4)=a-a+a-4=a-47x*((y-x)+3y)=7x(4y-x)=28xy-7x³4y-(3y+(2y(y+1)))=4y-(3y+2y²+2y)=4y-3y-2y²-2y=-2y²-y5c-(2c-((b-c)-2b))=5c-(2c-b+c-2b)=5c-2c+b-c+2b=2c+3b