3x(m-5x)=3mx- 15x^2=6x^2y^3+n

So:

3Mx=6x^2y^3

- 15x^2=N

So m = 6x 2y 3/(3x) = 2xy 3, n =- 15x 2.

4、

(1) in brackets = (-8a3+10a2+6a)/(-2a) = 4a2-5a-3.

(2) In brackets = (-4x3Y2+4x2Y2-6xy)/(2x2y-2xy+3)

=[(-2xy)*(2x^2y-2xy+3)]/(2x^2y-2xy+3)

=-2xy

5、

(x^2+ax+5)(-6x^3)

=-6x^5-6ax^4-30x^3

Because it does not contain x 4.

So, -6a=0.

So, a=0