In a chemical reaction, 20 units of a compound are injected into a reaction chamber every 30 min. Within that 30 min, 50% of the compound is used up in the chemical process. Suppose that the reaction starts at t = 0 with 20 units of the chemical in the chamber.

a) Make a table of values showing the amount of the compound remaining for the first 5 h, in 30-min intervals, that the reaction has been occurring.

b) Write the amount of the chemical remaining after each 30-min interval as a sequence.

c) Determine a recursion formula for the sequence.