def straightLine(x, m, c):
    """ A straight line model.
    
    Parameters
    ----------
    x : numpy list
        X positions.
    
    m : float
        Gradient.
    
    c : float
        Y-intercept.
        
    Returns
    -------
    Ys for a straight line.
    
    Examples
    --------
    x, m, c = [1, 2], 0.25, 1

    straightLine(x, m, c)
    >>> [1.25, 1.5]
    """
    return m*x + c