Differential Equations question help

[johnsmith123]

Can someone please help with this, the important point are:

Patient is given a drug at 200mg /kg of tissue: drug leaves the body at a rate proportional to x ( the amount of drug)
Find dx/dt (where x is amount of drug) basically set up differential equation

Then: if after 30 mins there is 50% of drug remaining solve differential equation

And finally: how long does it take for 10 percent of drug to remain

Thanks

[johnsmith123]

Much like this question, however not given the equation and given the condition that there is 200mg of x per 1 kg