Answer:
Possible numbers for Joshua's house are #13 and #21.
Explanation:
Given:
Vacation houses are equally spaced along a street.
The first house is marked with #10 and so on.
Maria lives in house marked as #17.
Joshua lives 4 houses away from Maria.
So, the difference between Joshua's house number and Maria's house number is 4.
Let 'x' be the house number of Joshua's house.
Case 1: If Joshua's house is after Maria's house. So,


Case 2: If Joshua's house is before Maria's house. So,


Therefore, the possible numbers for Joshua's house are #13 and #21.