Question 2. (2 marks) The median half-life for severe acute respiratory syndrome coro- navirus 2 (SARS-CoV-2) on plastic surfaces is 6.8 hours [1] (a) Construct a base e exponential model for the number of virus particles on a given plastic surface of the form n(t) = noe t, where time t is measured in hours, no is the number of virus particles on the plastic surface at t = 0, and r is the rate at which the virus population declines as a proportion of the current number of particles. (b) During a short, intense, bout of coughing, a person infected with SARS-CoV-2 coughs directly onto a nearby plastic surface three times, depositing 600 million virus particles (virions) onto the surface. In the absence of any external interference, such as cleaning, how long will it take after the bout of coughing for the number of virus particles on the plastic surface to reduce below one particle? [1] N van Doremalen, T Bushmaker, M G Holbrook, A Gamble, B N Williamson, A Tamin, J L Harcourt, N J Thornburg, S I Gerber, J O Lloyd-Smith, E de Wit, and V J Munster, Aerosol and Surface Stability of SARS-CoV-2 as compared with SARS-CoV-1, New England Journal of Medicine, 382(16):1564-1567, 2020