Question 330573
The assumption is that the cost of materials is based on the area of the disk (since the thickness is equivalent).
{{{T=C*A}}}, where {{{T}}} is total cost, {{{C}}} is cost per unit area, {{{A}}} is area.
The area of a circle is,
{{{A1=(pi/4)*D^2=(pi/4)*3^2=(9/4)*pi}}}
From the first example,
{{{0.15=C*(9/4)*pi}}}
{{{C=0.15/((9/4)*pi)}}}
The area for the second disk is,
{{{A2=(pi/4)*6^2=9pi}}}
Since A2 is 4 times as much as A1, then the total cost will be 4 times as much.
{{{T=((0.15)/((9/4)*pi))*(9*pi)=(0.15)(4)=0.60}}}
.
.
.
$0.60