1. **State the problem:** Brenda mixed 6 cans of blue paint with 7 cans of red paint to make purple paint for 1 wall. Dana wants to paint 4 identical walls with the same purple paint. We need to find how many cans of blue paint Dana needs. 2. **Understand the ratio:** The ratio of blue to red paint Brenda used is 6:7. This means for every 6 cans of blue paint, 7 cans of red paint are used. 3. **Calculate total paint for 1 wall:** Total cans for 1 wall = 6 (blue) + 7 (red) = 13 cans. 4. **Calculate total paint for 4 walls:** Since Dana wants to paint 4 walls, total cans needed = 4 \times 13 = 52 cans. 5. **Calculate blue paint needed for 4 walls:** Since blue paint is \frac{6}{13} of the total paint, blue paint needed = \frac{6}{13} \times 52. 6. **Simplify the expression:** $$\frac{6}{13} \times 52 = 6 \times \cancel{\frac{52}{13}} = 6 \times 4 = 24$$ 7. **Final answer:** Dana needs 24 cans of blue paint to paint 4 identical walls.