In the electricity part of the AP style problems, I think there is an error for #8. I think the initial current is 0.6 instead of .75. Shouldn't R2 and R4 be in series?
Then, R24 (combined) would be 2R. R234 (combined) would be in paralled and be 2R/3. Then, the Req would be R1+R234 (R+2R/3) which is 5R/3. Then wouldn't the current be 3/5? Not .75.