import matplotlib.pyplot as plt

# Use plot_grid(colleges_flipped) in your code!
def plot_grid(img):
    M = img.shape[0]
    N = img.shape[1]
    scale = 22
    
    # Plot the horizontal grid lines
    for k in range(1, M, scale):
        x = [1, N]
        y = [k, k]
        plt.plot(x, y, color='w', linewidth=1)
        plt.plot(x, y, color='k', linewidth=1)

    # Plot the vertical grid lines
    for k in range(1, N, 22):
        x = [k, k]
        y = [1, M]
        plt.plot(x, y, color='w', linewidth=1)
        plt.plot(x, y, color='k', linewidth=1)

    # Set axis limits
    plt.xlim(1, N)
    plt.ylim(1, M)

    plt.show()