Can someone please help with this and please show workings

2. A patient takes 500 mg of medication. Every 4 hours, 3/8 of the amount of medication is still present in the patient's system. A) Fill in the table. t (hours) A(t) (amount in mg) 0 4 8 B) Write an equation for the amount of medication after t hours have passed. C) If the patient must take another dose when the amount is 100 mg, how long before she must take another dose