1. **Stating the problem:** The family traveled 400 miles on the first day. We need to find the total length of their road trip and how many miles they still need to travel. 2. **Understanding the problem:** To solve this, we need the total length of the road trip. Since the problem does not provide the total length explicitly, we assume it is given or needs to be found from previous information. 3. **Formula and explanation:** If $T$ is the total length of the trip and $D$ is the distance traveled so far, then the remaining distance $R$ is: $$R = T - D$$ 4. **Applying the values:** Given $D = 400$ miles. - If the total length $T$ is known, substitute it to find $R$. 5. **Example:** If the total trip length is, for example, 1000 miles, then: $$R = 1000 - 400 = 600$$ miles still to travel. 6. **Summary:** - Total length of the trip: $T$ miles (needs to be known or given). - Distance traveled: 400 miles. - Distance remaining: $T - 400$ miles. Without the total length $T$, we cannot find the exact remaining miles. **Final answer:** - Total length of the trip: $T$ miles. - Miles still to travel: $T - 400$ miles.