There are 232 large, medium and small balls, worth 1,000 yuan. Among them, the number of small balls is 4 times that of the medium balls. The unit prices of large, medium and small balls are 21 yuan, 9 yuan, and 2 yuan respectively. How many big balls are there? indivual? (using equations)
有大、中、小球共232个，价值1000元，其中小球的数量是中球的4倍，大、中、小球单价分别是21元、9元、2元，那么大球有多少个？(用方程组)
<result>12</result>