Do you mean 3 red marbles and 2 blue marbles, and she's going to draw a marble 300 times?
The probability of drawing a red marble is 3/5 = 0.6.
The probability of drawing a blue marble is 2/5 = 0.4.
In 300 drawings, she should expect to draw a red marble 0.6 * 300 = 180 times.
She should expect to draw a blue marble 0.4 * 300 = 120 times.
