(1 point) Let
l
be the length of a diagonal of a rectangle whose sides have lengths
x
and
y
, and assume that
x
and
y
vary with time. If
x
increases at a constant rate of
(1)/(9)f(t)/(s)
and
y
decreases at a constant rate of
(1)/(4)f(t)/(s)
, how fast is the size of the diagonal changing when
x=1ft
. and
y=3ft
? Answer: