What is the time complexity of subset testing?

Consider the following problem:

Let $$A = \{a_1,…,a_n\}$$ and $$B = \{b_1,…,b_m\}$$ be two finite sets over $$\mathbb{N}$$. The sequences $$a_1,…,a_n$$ and $$b_1,…,b_m$$ do not have to be sorted. Given as inputs the strings $$a_1,…,a_n$$ and $$b_1,…,b_m$$, determine if $$A \subseteq B$$.

What is the time complexity of this problem?