What is the value of the expression 7.5(-1/2)?

Which of the following are accepted without proof in a logical system? check all that apply.

The number if marbles of different colors stored in a hat is listed below: 4 red marbles 10 green marbles 7 blue marbles. without looking in the hat, dan takes out a marble at random. he replaces the marble and then takes out another marble from the hat. what is the probability that dan takes out a blue marble in both draws?

Icould really use some with this question.