The correct option is C Both (a) and (b)
2x+3y=k and 6x+9y=12
a1=2,b1=3,c1=k
a2=6,b2=9,c2=12
a1a2=26,b1b2=39,c1c2=k12
If k=4,a1a2=b1b2=c1c2 i.e. lines are coincident and have many solutions
If k=36,a1a2=b1b2≠c1c2 i. e. lines are parallel and have no solution.