At the National Day Garden Party, there was a square team of 100 people, and each person in the square team held either red flowers or yellow flowers in their left hands. Each person's right hand either holds a red balloon or a green balloon. It is known that there are 42 people holding red flowers, 63 people holding red balloons, and 28 people holding yellow flowers in their left hand and green balloons in their right hands. Then how many people are holding a red flower in their left hand and a red balloon in their right hand?
国庆游园会上，有一个100人的方队，方队中每人的左手要么拿红花，要么拿黄花．每人的右手要么拿红气球，要么拿绿气球．已知拿红花的有42人，那红气球的有63人，左手拿黄花、右手拿绿气球的有28人．则左手拿红花，右手拿红气球的有多少人．
<gadget id="calculator">100 - 63</gadget>
<output>37</output>

<gadget id="calculator">37 - 28</gadget>
<output>9</output>

<gadget id="calculator">42 - 9</gadget>
<output>33</output>

<result>33</result>