观察下列关于自然数的等式：
（i）32﹣4×12=5 ①
（ii）52﹣4×22=9 ②
（iii）72﹣4×32=13 ③
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根据上述规律解决下列问题：
He will come to understand your efforts sooner or later. It's just a matter of_______.
