Given,
(αβγ)(2981034888)=(000)
⇒(2α+9β+8γ10α+3β+4γ8α+8β+8γ)=(000)
Now on comparing both side we get,
2α+2β+8γ=0…(1)
10α+3β+4γ=0…(2)
8α+8β+8γ=0…(3)
Now from (1) and (3) by cross multiplication we get,
1α=6β=−7γ=k⇒α=k,β=6k,γ=−7k
Point P(α,β,γ) lie on the plane 2x+4y+3z=5⇒2α+4β+3γ=5
⇒2k+24k−21k=5
⇒k=1
Hence, 6α+9β+7γ=6k+54k−49k=11k=11.