Write a function called polyplot that has one input array with three elements and no outputs. The array elements A, B, and C are coefficients of a polynomial equation y=Ax^3+Bx^2+Cx. The function should plot the equation with a red line and blue x's for markers. There should be 20 values of x varying from -5 to 5. The plot title is "Plot of y=Ax^3+Bx^2+Cx" where the characters A, B, and C are replaced with the actual values from the function input.