To find the point of intersection, substitute −7 for y in the equation y=−(x+3)2+9.−7=−(x+3)2+9−7=−x2−6x−9+9−7=−x2−6xx2+6x−7=0(x+7)(x−1)=0x=−7 or x=1Since PQ​ is on a horizontal line, y=−7,PQ=1−(−7)=8.