Answer:
13
Step-by-step explanation:
Mean would mean average, which in this case is 
so your equation would look like 
Next multiply both sides by to clear the fraction 
to get 
Subtract 69 from both sides 
you get 
Remember that if something is raised to a fraction exponent, the denominator of the fraction is the radical and the numerator stays a power. So it becomes:
fourth root of (48c)^3
Hope this helps
Based on the picture, PC = PD