Three forces act on a wheel of radius 20 cm as shown in fig.
 

The torques produced by forces 8N, 4N and 9N respectively are

$\mathrm{\tau }$₁ = 8N x 0.2m x sin30^o

    = 0.8 Nm (clockwise)

$\mathrm{\tau }$₂ = 4N x 0.2m x sin90^o(anticlockwise)

$\mathrm{\tau }$₃ = 9N x 0.2m x sin90^o (clockwise)

Net torque = 0.8 - 0.8+1.8 =1.8 Nm clockwise