The first digit will be 5 or 6 or 7 or 9
Total = 4 ways
The second digit will be any remaining number.
Total = 5 ways
The third digit will be only even numbers 2 and 6
Total = 2 ways
By the law of Multiplication the required number of digits "= 4 \\times 5 \\times 2 = 40"
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