Three balls are drawn at random from a bag containing \( 5 \) blue and \( 4 \) yellow balls. Let the random variables \( X \) and \( Y \) respectively denote the number of blue and yellow balls. If \( \overline{X} \) and \( \overline{Y} \) are the means of \( X \) and \( Y \) respectively, then \( 7\overline{X} + 4\overline{Y} \) is equal to _______.
