{ [ ( 2 × a + 3 ) × 2 + 3 ] × 2 + 3 } × 2 + 3 = 85
{ [ ( 2 × a + 3 ) × 2 + 3 ] × 2 + 3 } × 2 = 85 - 3
{ [ ( 2 × a + 3 ) × 2 + 3 ] × 2 + 3 } × 2 = 82
{ [ ( 2 × a + 3 ) × 2 + 3 ] × 2 + 3 } = 82 : 2
{ [ ( 2 × a + 3 ) × 2 + 3 ] × 2 + 3 } = 41
[ ( 2 × a + 3 ) × 2 + 3 ] × 2 = 41 - 3
[ ( 2 × a + 3 ) × 2 + 3 ] × 2 = 38
[ ( 2 × a + 3 ) × 2 + 3 ] = 38 : 2
[ ( 2 × a + 3 ) × 2 + 3 ] = 19
( 2 × a + 3 ) × 2 = 19 - 3
( 2 × a + 3 ) × 2 = 16
2 × a + 3 = 16 : 2
2 × a + 3 = 8
2 × a = 8 - 3
2 × a = 5
a = 5 : 2
a = 2, 5