The circular region with radius $R=6\mathrm{.}55cm$ shown in the figure has an electric field directed upwards and perpendicular to the region. The amount of electric flux ${}_E$ through a circle with radius $r$ from the center of the region is given by the expression

${}_E(r)=(2\mathrm{.}25V)r$

What is the magnitude $B$ of the induced magnetic field at a distance $r=5\mathrm{.}75cm$ from the center of the circular region?

$B=$