Because 72x=[]46[],

72=2×2×2×3×3=8×9,

So []46[] can be divisible by 8 and 9, and also by 8, so the last three digits should be divisible by 8, so 46X can be divisible by 8, and x = 4； is obtained;

If it can be divisible by 9, the sum of digits of a number can be divisible by 9, so Y+4+6+4 can be divisible by 9, so x = 4；;

That is, 72x=[4]46[4],

x = 62

A: A * * * There are 62 participants;

So the answer is: 62.