Model reservoir inflow and quadratic outflow

During rainfall, a reservoir contains $x$ million cubic metres at time $t$ hours. Inflow is constant at $k$ million cubic metres per hour, and outflow is proportional to $x^2$.

(i) Given that the water amount stabilises at $0.5$ million cubic metres, show that $dx/dt=k(1-4x^2)$.

(ii) Find $x$ in terms of $k,t$ if initially there is $1$ million cubic metre.