220 cm2/s
EXPLINATION
L length of rectangel (cm)
W width of rectangel(cm)
A area of rectangel (cm²)
T time (s)
we are told that:
d1\dt=8cm\s(const),and dw\dt =3cm\s(const)
the area of the rectangel is
A=LW
Differentiating wrt t (using the product rule) we get;
dAdt=(l)(dwdt)+(dldt)(w)
∴dAdt=3l+8w
So when l=20 and w=10⇒
dAdt=3⋅20+8⋅20
∴dAdt=60+160
∴dAdt=220 cm2/s
