A study was conducted on the sales of DVD players and VHS players between 1997 and 2009. The number of DVD players was v(t) = = t3 - 5t + 4000 thousands where t corresponds to the number of years since 1997. The number of VHS players was d(t) = 6 + 7 thousands where t corresponds to the years since 1997. a) Find the rule for the function r(t) that represents the ratio of DVD players sold to the number of VHS players sold at any moment, in terms of the number of years elapsed since 1997. b) Find r(4) and then explain what it represents in this context. c) Find the end behavior of the function r and explain what it means in this context.