The expression in the image is:

$\sqrt{64} - \sqrt{25}$

To solve this:

1. First, find the square root of 64: $\sqrt{64} = 8$

2. Next, find the square root of 25: $\sqrt{25} = 5$

3. Subtract the results: $8 - 5 = 3$

So, the value of the expression $\sqrt{64} - \sqrt{25}$ is 3.

Would you like more details or have any questions?

Here are 5 related questions for further practice:

1. What is the value of $\sqrt{144} - \sqrt{81}$?
2. Simplify $\sqrt{49} + \sqrt{16}$.
3. Calculate the difference: $\sqrt{36} - \sqrt{9}$.
4. Find the value of $\sqrt{100} + \sqrt{25}$.
5. Simplify the expression: $\sqrt{121} - \sqrt{64}$.

Tip: Remember, the square root of a number $x$ is a number $y$ such that $y^2 = x$.