Question

B={x aparține luiN|7 <SAU EGAL cu 7x <SAU EGAL cu21}

Answer 1

7≤7x
x ≥ 1
si
7x ≤ 21
x ≤ 21:7
x ≤ 3
si x∈N
x ∈{1, 2, 3}