1. **State the problem:** We need to find the expression that represents the perimeter of Humberto's backyard, which is a rectangle with length $x + 6$ and width $2x - 1$. 2. **Recall the formula for the perimeter of a rectangle:** $$\text{Perimeter} = 2(\text{length} + \text{width})$$ 3. **Substitute the given expressions:** $$P = 2((x + 6) + (2x - 1))$$ 4. **Simplify inside the parentheses:** $$P = 2(x + 6 + 2x - 1)$$ $$P = 2(3x + 5)$$ 5. **Distribute the 2:** $$P = 2 \times 3x + 2 \times 5$$ $$P = 6x + 10$$ 6. **Conclusion:** The expression representing the perimeter is $6x + 10$. Therefore, the correct answer is **6x + 10**.