b) get out your graphing calculator and graph v(t) in Y1 ... don't forget to use x for t and 2 for vo. graph 10% of 2 = .2 in y2 so you can see where the two graphs intersect and solve for t.
c) set the left side equal to 1 (half of 2, right?)
divide both sides by 2
take the natural log (ln) of both sides
solve for t