Pg 316(328) - Q23
You've got to step back from this one. What is the average of X,Y, and Z? Well, it's what you've got right there in the parentheses:(X+Y+Z)/3. So, you've got that value of the average right there, and that average is being multiplied by 4. Therefore, if you divide both sides by 4, you have P/4 equals that average and that correlates to answer D.