You didn't say how exactly your R and C are hooked up, where the power supply is connected, and where Vtg is measured.
What course is this for? Where are you going to school? What is your major? What year are you in?
I'm not going to do your homework for you. You need to do a few things on your own. Look up something called the RC time constant. Note that resistance times capacitance is time. When the resistance is in Ohms and the capacitance in Farads, then the resistance x capacitance product is a value in seconds. A RC circuit will relax e times closer to its final state in that many seconds.
Now, can you write the equation for that?
