There are 232 large, medium and small balls, worth 1,000 yuan, and the number of small balls is 4 times that of the medium balls. It is known that the unit prices of large, medium and small balls are 21 yuan, 9 yuan, and 2 yuan respectively, so how many big balls are there?
有大、中、小三种球共232个，价值1000元，其中小球的数量是中球的4倍．已知大、中、小三种球单价分别是21元、9元、2元，那么大球有多少个．
<result>12</result>