Question

 A= {x} x Є N e 20 ≤ x < 35}

Answer 1

.
$A=\{x\in N ~e~20 \leq x<35\} \\ \\ A=\{20,21,22,23,24,25,26,27,28,29,30,31.32,33,34\}$

$B=\{x\in N~e~x+1=2x\} \\ \\ x+1=2x \\ x-2x=-1 \\ -x=-1 \\ x=1 \\ \\ B=\{1\}$