What equation represents the relationship between time upstream and time downstream given a time difference of 3?

To understand why the correct answer is the one that states the relationship as Tu - Td = 3, it is essential to clarify what Tu and Td represent. Here, Tu denotes the time it takes to travel upstream, while Td indicates the time it takes to travel downstream.

The premise of the question indicates that there is a time difference of 3 between the time spent upstream and the time spent downstream. This means if one goes upstream, it takes a certain amount of time longer than it does to come back downstream.

When you denote the greater time spent upstream as Tu, the relationship between the times can be defined clearly by stating that the time moving upstream minus the time moving downstream equals the difference of 3. In algebraic form, this is expressed as Tu - Td = 3.

This equation effectively conveys that when you subtract the time taken downstream from the time taken upstream, the result is a difference of 3 units of time. Thus, it correctly captures the relationship posed in the question.

Understanding this relationship not only clarifies the problem at hand but also highlights how time differences can be algebraically represented in terms of complementary activities such as traveling upstream versus downstream.