Suppose that it takes $3 \cdot 10^9$ seconds to examine each key in a list. If there are $n$ keys and we search through them in order until we find the right one, find

1. the worst-case complexity

Worst case is $n \cdot 3 \cdot 10^{-9}$ seconds

2. the average-case complexity

Average case is $\frac{n+1}{2} \cdot 3 \cdot 10^{-9}$ seconds