The length $x$ of a rectangle decreases at $3$ cm/min and the width $y$ increases at $2$ cm/min. When $x=10$ cm and $y=6$ cm, the rate of change of the area is

1. $\dfrac{dx}{dt}=-3$, $\dfrac{dy}{dt}=2$, $x=10$, $y=6$. 2. Area $A=xy$, so $\dfrac{dA}{dt}=\dfrac{dx}{dt}\,y+x\,\dfrac{dy}{dt}$. 3. $=(-3)(6)+(10)(2)=-18+20=2$. 4. The trap $38$ adds magnitudes instead of using signs. _Source: NCERT Class 12 Mathematics Ch 6 "Application of Derivatives", p.2_