An office machine is purchased for $7900. Assume that its salvage value, V, in dollars, depreciates, according to a method called double declining balance, by 20% each year and is given by V(t)=7900(0.80), where t is the time, in years, after purchase. a) Find V(7), and explain its meaning. b) Find V'(7), and explain its meaning. c) When will the salvage value of the office machine be half of the purchase price? a) V(7)=$ (Round to the nearest cent as needed)