Work Step by Step
Since all houses are evenly spaced, let's call the distance between 2 neighboring houses, which is the same for all pairs of neighboring houses, $L$. To walk from the first house to the third house, you need to walk for $2L$, ($L$ from the first to the second and $L$ from the second to the third.) To walk a full circle, you need to walk for 6 $L$s. (first to second, second to third, third to fourth, fourth to fifth, fifth to sixth, and sixth to first) We know it takes $10$ minutes to walk $2L$. That means that it takes $10\div2=5$ minutes to walk one L. The time it takes to walk a full circle is then: $5*6=30$ minutes.