a =4. 36:a=8×2-7
a=36:9
a=4
( 36 : a + 63 : 9 ) : 2 = 8
( 36 : a + 7 ) : 2 = 8
36 : a + 7 = 8 × 2
36 : a + 7 = 16
36 : a = 16 - 7
36 : a = 9
a = 36 : 9
a = 4
