An Airline flies directly from Istanbul to Housten and numbers its coach fare classes from higher to lower as $1,2$ and $3.$ The airline has zoo seats in the coach class. The ticket prices for the classes are P$1=600,$ P$2=400,$ P$3=200.$ D$($i$)$ denotes the demand for fare class i$.$ The airline considers the cumulative demands.

D$1=$ D$1,$  D$1,2=$ D$1+$ D$2,$  D$1,2,3=$D$1+$ D$2+$ D$3$

D$1$  in $(50,100),$  D$1,2$  in $(100,200),$  D$1,2,3$  in $(150,300)$

Apply EMSR$-$b heuristic to find the protection levels for the classes.

A$)$ What are the aggregate prices p$1,2$ and p$1,2,3?$

B$)$ What is the protection level y$2$ for classes $(1,2)?$

C$)$ What is the protection level y$1$ for classes $(1)?$