a) (24x\(^4\)y\(^3\)- 30\(x^5y^2\)- 6 \(x^6y^3\)) : 6\(x^4y^2\)
= (24\(x^4y^3\): 6\(x^4y^2\)) - (30\(x^5y^2\): 6\(x^4y^2\)) - (6\(x^6y^3\): 6\(x^4y^2\))
= 4y - 5x - x\(^2\)y
b) (x-3)(x+3)- (x-2)(x+1)
= x\(^2\)- 9 - (x\(^2\)+x-2x-2)
= x\(^2\)- 9 (x\(^2\)- x -2)
= x\(^2\)- 9 -x\(^2\)+ x+2
= -7+x