If force is applied at 30 degree with the horizontal
then first we will find the components of force in two directions
[tex]F_x = 20 cos20[/tex]
[tex]F_y = 20 sin30[/tex]
now we can find normal force by balancing the forces in Y direction
[tex]F_n + Fy = mg[/tex]
[tex]F_n + 20 sin30 = 3*10[/tex]
[tex]F_n + 10 = 30[/tex]
[tex]F_n = 20 N[/tex]
now since block is moving with constant speed
so here forces along horizontal plane will be balanced also
[tex]F_x = F_f[/tex]
[tex]F_f = 20 cos30[/tex]
[tex]F_f = 17.3 N[/tex]
Now the weight of the box is defined as
[tex]W = mg[/tex]
now plug in all values
[tex]W = 3*10 = 30 N[/tex]
