`a) 4x^2-6x+m`
`=4x^2-12x+6x-18+m+18`
`=4x(x-3)+6(x-3)+m+18`
`=(x-3)(4x+6)+m+18`
Để `A(x) \vdots B(x)`
`=> m+18 \vdots x-3`
`<=>m+18=0`
`<=> m=-18`
Vậy `m=-18`
`c) x^3+3x^2+5x+m`
`=x^3+3x^2+5x+15+m-15`
`=x^2(x+3)+5(x+3)+m-15`
`=(x+3)(x^2+5)+m-15`
Để `A(x) \vdots B(x)`
`=> m-15 \vdots x+3`
`<=> m-15=0`
`<=> m=15`
Vậy `m=15`
`h) 3x^2+mx+27`
`=3x^2+15x+(m-15)x+5(m-15)+27-5(m-15)`
`=3x(x+5)+(m-15)(x+5)+27-5(m-15)`
`=(x+5)(3x+m-15)+27-5(m-15)`
Để `3x^2+mx+27 \vdots x+5`
`=> 27-5(m-15) \vdots x-5`
`<=> 27-5(m-15)=0`
`<=> 27-5m+75=0`
`<=> 102-5m=0`
`<=> 5m=102`
`<=> m=102/5`
Vậy `m=102/5`