Answer: the known variable; the to-be-predicted variable
Explanation:
In statistics, linear regression is a technique to model the relationship between two variables ( one independent and other dependent).
It requires some previous data to plot a best fit line.
It is used to predict the values for dependent variable for each independent variable.
Here, independent variable = known variable and dependent variable = is to be predicted
Hence, Linear regression describes the extent to which the known variable predicts the to-be-predicted variable.