Rate of change (1 Viewer)

[JustinLee]

The length of a rectangle is being decreased at the constant rate of 4cm/s whilst the breadth is increased in such a way that the figure remains a rectangle of fixed area 60 cm². What is the rate of change of the
1) breadth
2) perimeter,
When the length is 12cm?

Thanks for help!

 

[Drongoski]