a) `4x^2y.(3x^3+xy^2 -1/4y)`

`=4x^2y .3x^3 +4x^2y .xy^2 - 4x^2y .1/4y`

`=(4.3).(x^2 .x^3).y+4.(x^2 .x).(y.y^2) - (4. 1/4).x^2 .(y.y)`

`=12x^5y+4x^3y^3-x^2y^2`

``

b) `(-5x^2y^4).(2xy+y^2-yz`

`=-5x^2y^4 . 2xy - 5x^2y^4 .y^2 + 5x^2y^4 .yz`

`=(-5. 2).(x^2 .x).(y^4 .y) - 5. x^2 .(y^4 .y^2) + 5.x^2 .(y^4.y) .z`

`=-10x^3y^5-5x^2y^6 +5x^2y^5z`

``

c) `(2x^3 -3xy+y) . 2/3 x^2yz`

`=2x^3 . 2/3 x^2yz-3xy. 2/3 x^2yz+y. 2/3 x^2yz`

`=(2. 2/3).(x^3 .x^2) .yz - (3. 2/3).(x.x^2) .(y.y).z+2/3 x^2 .(y.y).z`

`=4/3x^5yz-2x^3y^2z+2/3x^2y^2z`