def payoff_call(underlying, strike, gearing=1.0):
    """payoff_call
    Payoff of call option.

    :param float underlying:
    :param float strike:
    :param float gearing: Coefficient of this option. Default value is 1.
    :return: payoff call option.
    :rtype: float
    """
    return gearing * max(underlying - strike, 0)