Related Rates: Growing Rectangle

[-thesignpainter]

I had a question just like this and I was completely stuck. Somehow I didn't recognize that I needed to use product rule, thanks

[juansalas]

why do people say you apply the chain rule here too?

[rashedalali]

Thank you a lot, you really helped me, keep it up.

[rauxacc]

Thank you so much. This helped me a lot.

[faresabowandi]

Is this considered taking partial derivatives?(because (A) depends on two variables)