Question 976137
{{{A=4pi*r^2}}}, your surface area formula, variable being r.


{{{dA/dt=4pi*2r*(dr/dt)}}}
{{{dA/dt=8pi*r(dr/dt)}}}
Chain Rule is used because radius r is a function of time, and using t for time variable.


Your example specifically specified, {{{dr/dt=3}}}, in cm squared per second.