The length $x$ of a rectangle decreases at $3$ cm/min and the width $y$ increases at $2$ cm/min. The rate of change of the perimeter is

1. $\dfrac{dx}{dt}=-3$, $\dfrac{dy}{dt}=2$. 2. Perimeter $P=2(x+y)$. 3. $\dfrac{dP}{dt}=2\left(\dfrac{dx}{dt}+\dfrac{dy}{dt}\right)=2(-3+2)=-2$. _Source: syllabus Mathematics Ch 6 "Application of Derivatives", p.2_