Suppose we are drilling into an up dip $($tilted$)$ gas formation at $4,000ft.$ The WGC $($water gas contact$)$ is at $8,000ft.$ and the pressure is "normal at $8,000ft$ and also normal outside the formation at $4,000ft.$ The temperature is assumed constant at $160F$ and the gas gravity is $0\mathrm{.}78.$ We are using the appropriate mud weight for balanced drilling at $3,999$ ft $($before we "hit" the gas formation.$)$

a$.$ What is the appropriate mud weight at $3,999?$

b$.$ What is the gas pore pressure at $4000ft$ inside the formation? $($You may assume $Z=\mathrm{.}96...$ although don't forget you are supposed to know how to calculate Z$...)$

c$.$ What mud weight do we need to be balanced when we$-$drill into the formation?