Transistor electronic circuit design problem + Sensitivity Analysis?

Attached is a brief description of a circuit model using two transistors. It has relevance to a voltage regulator circuit. Number 2 is most important. You can answer all if you want. If more information is needed ask. What is R6 doing there? You can ignore... show more Attached is a brief description of a circuit model using two transistors. It has relevance to a voltage regulator circuit. Number 2 is most important. You can answer all if you want. If more information is needed ask. What is R6 doing there? You can ignore R6.

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