Can't comment on the exam as I'm not taking it.
Regarding the question, I presume you're familiar with "suvat", or some permutation of that acronym.
I'd use s=ut+1/2 at^2 as your basic equation.
Form an equation for how far it travels upto the final second.
And form an equation as to how far it falls in total.
Then elminate s between the two equations to get t (yes, it's a quadratic).
Etc.
Post working if you're still stuck