原式= 5/3 *(21/10 + 7/ (37/12 - 13/8)) = 5/3 * ( 21/10 + 7/ (35/24)) = 5/3 * ( 21/10 + 24 /5 ) = 5/3 * 69 / 10 = 23/2 = 11又二分之1
