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?