How many non-negative integral values of $x$ satisfy the equation  $ \lfloor \frac{x}{5}\rfloor = \lfloor \frac{x}{7}\rfloor $
To find the non-negative integral values of \( x \) that satisfy the equation \( \left\lfloor \frac{x}{5} \right\rfloor = \left\lfloor \frac{x}{7} \right\rfloor \), we need to analyze the behavior of the floor functions.

1. **Understanding the Floor Function:**
   The floor function \( \left\lfloor y \right\rfloor \) returns the greatest integer less than or equal to \( y \). Therefore, for \( \left\lfloor \frac{x}{5} \right\rfloor \) and \( \left\lfloor \frac{x}{7} \right\rfloor \) to be equal, the values of \( \frac{x}{5} \) and \( \frac{x}{7} \) must lie within the same integer interval.

2. **Setting Up the Inequality:**
   Let \( k \) be the common value of the floor functions. Then:
   \[
   k \leq \frac{x}{5} < k+1 \quad \text{and} \quad k \leq \frac{x}{7} < k+1
   \]
   This implies:
   \[
   5k \leq x < 5(k+1) \quad \text{and} \quad 7k \leq x < 7(k+1)
   \]

3. **Finding the Intersection:**
   For both inequalities to hold simultaneously, \( x \) must lie in the intersection of the intervals:
   \[
   \max(5k, 7k) \leq x < \min(5(k+1), 7(k+1))
   \]
   Since \( 7k \geq 5k \), the intersection simplifies to:
   \[
   7k \leq x < \min(5k + 5, 7k + 7)
   \]

4. **Determining the Range:**
   We need to find the values of \( k \) for which the intersection is non-empty. Let's analyze the intervals for different values of \( k \):

   - For \( k = 0 \):
     \[
     0 \leq x < 5
     \]
     Possible values: \( 0, 1, 2, 3, 4 \)

   - For \( k = 1 \):
     \[
     7 \leq x < 10
     \]
     Possible values: \( 7, 8, 9 \)

   - For \( k = 2 \):
     \[
     14 \leq x < 15
     \]
     Possible value: \( 14 \)

   - For \( k \geq 3 \):
     The intervals do not overlap because \( 7k \geq 5(k+1) \).

5. **Combining the Results:**
   The non-negative integral values of \( x \) that satisfy the equation are:
   \[
   \{0, 1, 2, 3, 4, 7, 8, 9, 14\}
   \]

The final answer is \(\boxed{0, 1, 2, 3, 4, 7, 8, 9, 14}\)