Leave cm alone the range of the circle at time

Pace of increment of span of circle = 3 cm/sec

dx/dt is positive and = 3 cm/sec

Let y be the space of the circle.

Pace of progress of space of circle =

=

= 

Putting = 10 cm (given),dy/dt

= cm2/sec

Since dy/dt  is positive, along these lines surface region is expanding at the pace of cm2/sec.