I'm confused by this question and do not know where to start. If I use the chain rule and write $\displaystyle \frac{dB}{dt} = \frac{dB}{dx} \times \frac{dx}{dt}$ , where $\displaystyle B$ is the length of the floor from the wall to point $\displaystyle B$ and where $\displaystyle t$ is the time, what would $\displaystyle x$ be?A ladder $\displaystyle AB$ of length $\displaystyle 5$ metres has one end $\displaystyle A$ leaning against a vertical wall. The other end $\displaystyle B$ rests on horizontal ground. When $\displaystyle A$ is at a height of $\displaystyle 4$ metres, it slides down the wall at a rate of $\displaystyle 2 m/s$. How fast is the other end, $\displaystyle B$, sliding along the horizontal ground? Answer: $\displaystyle \frac{8}{3}m/s$

I only know that when A is at a height of 4 metres, B must be at 3 metres away from the wall because of the pythagora's theorem.

Any help would be appreciated and thank you in advance.