Answer
$t$ is the input which is the year;
$P(t)$ is the output which is the price of Nike shoes, in dollars;
the relation is not a function
Work Step by Step
In the given, the input variable is the year, $t$, in years, and the output is the price of Nike shoes, $P(t)$, in dollars.
Some ordered pairs, $(t,P(t))$, that represent this situation are $(2000, \$200)$ and $(2000,\$300)$. This means that in the year $2000$ the price of a pair of Nike shoes is \$$200$ while another pair of Nike shoes has a price of \$$300$.
In the example of ordered pairs above, the first coordinate was repeated. Since the ordered pairs in functions should not have first coordinates that repeat, then the given situation does not describe a function.
