what expression does this set of algebra tiles represent?

Explanation:

Step1: Count $x^{2}$ - tiles

There are 8 blue tiles with $x^{2}$ on them, so the term for $x^{2}$ is $8x^{2}$.

Step2: Count $x$ - tiles

There is 1 green tile with $x$ on it, so the term for $x$ is $x$.

Step3: Count unit - tiles

There are 5 yellow tiles with 1 on them, so the constant term is 5.

Answer:

$8x^{2}+x + 5$