The answer to #6 is correct, as long as you include the correct units (amps? volts? ohms?)
question 7 & 8 – we do show you this exact calculation in the last video in Unit 3.
We also gave you this hint in the explanation that shows up in your quiz results:
“P = I^2 * R You need to use the total circuit current and the resistance of the particular load of interest, in this case, R2.” (or R1, for #8)
If these don’t help you, you’ll need to show me how you’re doing the calculation so I can see where the mistake is.