Write a MATLAB script to generate x-values from -3 to 3 using linspace with 150 value in plot. Define four different y-values as follows:

1. y1=sin(x)
2. y2=cos(x)
3. y3=sin(x)cos(x)
4. y4=21cos(2x)

Plot these four curves on the same graph using different line styles and colors. Include appropriate labels for the x-axis and y-axis, a title for the plot, and a legend.