Relevance means that your changes will also have an impact on it. If there are several identical apples, the same pears and the same bananas in a bag, when the number of apples changes, the total weight of the bag changes, which is caused by the change of apples, then this is relevance. Is to connect with each other.

In direct proportion, if there are only apples in the bag, the number of apples is linear with the weight of the bag.

When x*b=y, b is a fixed value, such as the quality of apples above, and x is a variable value, such as the number of apples above. Y is the total weight, so the change of the number of X apples directly affects the change of Y. The degree of change, such as adding an apple at a time, is the weight of an apple, which is a fixed value.