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Answer
The actual question is 7,9,(30),4,5; 17,8,(50),6,3; 10,21,(?)6,3
Now consider the 1st block
1. 7,9,(30),4,5
The expression is
2(7+9+4+5)-(4x5)
2(25)-20
50-20=30
Similarly,
2. 17,8,(50),6,3
2(17+8+6+3)-6x3
68-18=50
Now, 10,21,(?)6,3
2(10+21+6+3)-(6x3)
80-18
=62
