126-?÷25×28.7＝12.5求问号数字.

先乘除,后加减
126 - A ÷ 25 × 28.7 ＝ 12.5
126 - (A ÷ 25 × 28.7) = 12.5 [先乘除,刮起来成为一体]
126 - 12.5 = (A ÷ 25) × 28.7 [等式左右互换,加变减,乘变除]
113.5 = (A ÷ 25) × 28.7
113.5 ÷ 28.7 = A ÷ 25
113.5 / 28.7 = A / 25
(113.5 x 25) / 28.7 = A
A = 28375/287 = 98又 249/287 = 98.86759581881533