(a(i))[1]
Express, in terms of $x$, how many hours he needs.
(a(ii))[4]
Set up an equation in terms of $x$ and show that it simplifies to $x^2-4x-32=0$.
(a(iii))[3]
Solve $x^2-4x-32=0$ using factorisation.
(a(iv))[2]
Determine how many hours Yuki needs to walk the 12 km route.
(b)[3]
Calculate the bus's lower bound for speed.