Maths Identities HELP THX

3(2c-d)X+c-d = 18X + 1
(6c-3d)X + c-d = 18X + 1
=>6c-3d = 18 ------------- (1)
and c-d = 1
=>c = d+1 ------------(2)

sub (2) into (1) we get
6(d+1) - 3d = 18
=> 6d + 6 - 3d = 18
=> 3d = 12
=> d = 4 ---------- (3)

sub (3) into (2) we get
c = 4 + 1 = 5

3(2c-d)x+c-d=18x+1
18x+1
18÷3=6
6=2c-d

假設c=3 d=3
2×3+3=9 3×9=27 不成立

9分成5及4
3(2×5-4)X+5-4=18X+1
=3x6X+1=18X+1
=18X+1=18X+1 成立