And explain how to do it if you can : )

Graph C.

Step-by-step explanation:

If you calculate f for x=0, you get f(0)=3*1=3. This rules out answer A already.

Next, you can expect the graph to approach y=0 for large x. The larger the x, the more times you're multiplying by 0.5. Graph C is the only one that does that. So even without actually graphing it, you know that C is the one.