3a-5b+19=0,a+8b-1=0
两式相加,得4a+3b+18＝0,即4a+3b＝-18
(4a+3b)^2-8a-6a＝(4a+3b)^2-2*(4a+3b)=(4a+3b)(4a+3b-2)=(-18)*(-20)=360