Use mathematical induction in Exercises $38-46$ to prove results about sets.
Prove that if $A_{1}, A_{2}, \ldots, A_{n}$ and $B_{1}, B_{2}, \ldots, B_{n}$ are sets such that $A_{j} \subseteq B_{j}$ for $j=1,2, \ldots, n,$ then
$$
\bigcup_{j=1}^{n} A_{j} \subseteq \bigcup_{j=1}^{n} B_{j}
$$