Alab researcher wants to find out whether mice will run through a maze quicker during the day or at night, after training. describe what is being measured in this experiment and what variable is being manipulated?

The goal of any experiment is to test the hypothesis by adjusting the independent variables so you can see the trend of the dependent variable that you want to investigate. The independent variables are parameters that you manipulate. In this experiment, that would be the time of day. You have two independent variables: night and day. The speed of the mice is the parameter that you will measure. Once you do these set-up, you can conclude in the end the effect of the time of day on the speed of the mice. 

3x+9+4x+x=8x+9that's the answer for your question.