C# Referencing the return value of a boolean method in another boolean method

I would like to know how to use the result of a boolean method in another method. The code below contains two methods, one named ValidateDay and another called IsLeapYear. IsLeapYear determines if a user entered integer is a leap year. ValidateDay checks if the day a user enters is a valid day based on what number month the user entered. In order the check if Feb 29th is a valid day, I need the ValidateDay method to know if the result of IsLeapYear is true or false. However, I am not sure how to reference the return value of IsLeapYear in the ValidateDay method. Any advice would be greatly appretiated.

// Determines if day is valid
    public Boolean ValidateDay()
    {
        IsLeapYear();

        if(Month == 1 || Month == 3 || Month == 5 || Month == 7 || Month == 8 || Month == 10 || Month == 12)
        {
            if (Day >= 1 && Day <= 31)
            {
                return true;
            }
            else
            {
                return false;
            }
        }
        else if (Month == 4 || Month == 6 || Month == 9 || Month == 11)
        {
            if (Day >= 1 && Day <= 30)
            {
                return true;
            }
            else
            {
                return false;
            }
        }
        else if (Month == 2 && IsLeapYear(true))
        {
            if (Day >= 1 && Day <= 29)
            {
                return true;
            }
            else
            {
                return false;
            }
        }
        else if (Month == 2 && IsLeapYear(false))
        {
            if (Day >= 1 && Day <= 28)
            {
                return true;
            }
            else
            {
                return false;
            }
        }
    }

    // Determine if year is a leap year
    public Boolean IsLeapYear()
    {
        if ((Year % 4 == 0 && Year % 100 != 0) || (Year % 400 == 0))
        {
            return true;
        }
        else
        {
            return false;
        }
    }