A Stone Is Dropped into a Lake, Creating a Circular $45 \mathrm {~cm} / \mathrm { s }$

Short Answer

A stone is dropped into a lake, creating a circular ripple that travels outward at a speed of $45 \mathrm {~cm} / \mathrm { s }$ . Express the radius $r$ of this circle as a function of the time $t$ (in seconds) and find $A \circ r$ , if $A$ is the area of this circle as a function of the radius.