We know x = 4 + y (1)
So 2x - 3y = 1
<=> 2.(4 + y) - 3y = 1
<=> 8 + 2y - 3y = 1
<=> 8 - y = 1
<=> y = 8 - 1
<=> y = 7 (2)
move (2) to (1) : x = 7 + 4 = 11
ok done. Thank to me :>
