[(72×a-80):2+2×124]:4=97
[(72×a-80):2+2×124]=97×4
(72×a-80):2+2×124=388
(72×a-80):2 +248=388
(72×a-80):2=388-248
(72×a-80):2= 140
72×a-80=140×2
72×a-80=280
72×a=280+80
72×a=360
a=360÷72
a=5
