PLEASE HELPLaw of sines: Which represents the value of c?

Answer:  3sin(45) over sin(40)

Using the law of sins that is given, you can write the following proportion.
3/sin(40) = c/sin(45)

All you have to do to solve for C is to multiply by sin(45). In the proportion, the letter are the side lengths and the trig ratios are of the angle opposite the side.