What is the plane equation passing through the intersection line ax+ by + cz + d = 0, a1x+ b1y + c1z + d1 = 0

what is the plane equation passing through the intersection line ax+ by + cz + d = 0, a1x+ b1y + c1z + d1 = 0 and is also perpendicular to XOY plane?

Any plane passing through the line of intersection of ax+by+cz+d=0 and a1x+b1y+c1z+d1=0 will be of the form (ax+by+cz+d)+k(a1x+b1y+c1z+d1)=0. This plane perpendicular to XOY plane whose direction cosines are (0,0,1). Using the condition for perpendicularity of two planes we get c+kc1 = 0, which gives k = -c/c1. Thus the required equation of the plane is
(ax+by+cz+d) + (-c/c1)(a1x+b1y+c1z+d1)=0.