(c) $A \cap B = \left\{ x:x\ a\ multiple\ of\ 3 \right\} and\ \{ x:x\ is\ \ a\ multiple\ of\ 5\}$ $= \{ x:x\ is\ a\ multiple\ of\ 15\}$ $\ \ \ \ \ \ \ \ \ \ \ \ = \{ 15,\ 30,\ 45,\ldots\ldots\ldots.\}$
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.