bantuin kak ... please butuh banget

-b/2a=4
-(3a-20)/(2(a-3))=4
-3a+20=8a-24
44=11a
a=4

f(x)=x²-8x-36

y=-D/4a=-(b²-4ac)/4a=-((-8)²-4(1)(-36))/4(1)=-52

jadi, nilai ekstrim P(x;y) =>(4;-52)