A street has parallel curbs $ 40$ feet apart. A crosswalk bounded by two parallel stripes crosses the street at an angle. The length of the curb between the stripes is $ 15$ feet and each stripe is $ 50$ feet long. Find the distance, in feet, between the stripes. 

$ \textbf{(A)}\ 9 \qquad \textbf{(B)}\ 10 \qquad \textbf{(C)}\ 12 \qquad \textbf{(D)}\ 15 \qquad \textbf{(E)}\ 25$
1. **Identify the given information and the goal:**
   - The distance between the parallel curbs is \(40\) feet.
   - The length of the curb between the stripes is \(15\) feet.
   - Each stripe is \(50\) feet long.
   - We need to find the distance between the stripes.

2. **Visualize the problem:**
   - Draw a diagram with two parallel lines representing the curbs.
   - Draw two parallel lines representing the stripes crossing the curbs at an angle.
   - Label the distance between the curbs as \(40\) feet.
   - Label the length of the curb between the stripes as \(15\) feet.
   - Label the length of each stripe as \(50\) feet.

3. **Formulate the problem using similar triangles:**
   - Consider the right triangle formed by one stripe, the distance between the curbs, and the distance along the curb between the stripes.
   - This triangle has sides \(30\) feet (half of the distance between the curbs), \(40\) feet (the distance between the curbs), and \(50\) feet (the length of the stripe).

4. **Set up the similar triangles:**
   - The larger triangle is a \(30\)-\(40\)-\(50\) triangle.
   - The smaller triangle is formed by the distance \(x\) along the curb between the stripes, the distance \(y\) between the stripes, and the length of the curb between the stripes \(15\) feet.

5. **Use the properties of similar triangles:**
   - The ratio of the sides of the similar triangles is the same.
   - Therefore, we have:
     \[
     \frac{y}{40} = \frac{15}{50}
     \]

6. **Solve for \(y\):**
   \[
   \frac{y}{40} = \frac{15}{50}
   \]
   \[
   \frac{y}{40} = \frac{3}{10}
   \]
   \[
   y = 40 \times \frac{3}{10}
   \]
   \[
   y = 12
   \]

7. **Verify the solution:**
   - The distance between the stripes is \(12\) feet, which matches the given conditions and the properties of similar triangles.

The final answer is \(\boxed{12}\)