Assuming
1) A coordinate system with origin at the force vec F→F application point
2) Brass plate with unknown mass distribution.
Calling
vec F_A = 3.5(cos 40^@, sin 40^@)→FA=3.5(cos40∘,sin40∘)
vec F_B = 2.8(-cos 50^@, sin 50^@)→FB=2.8(−cos50∘,sin50∘)
vec F_G = m g (0,-1)→FG=mg(0,−1)
vec F = f(-1,0)→F=f(−1,0)
O = (0,0)O=(0,0)
A = (0,1)A=(0,1)
B = (2.5,1)B=(2.5,1)
G =(x_G,y_G)G=(xG,yG) Brass plate mass center
we have
Null force resultant
vec F_A+vec F_B+vec F_G+ vec F = vec 0→FA+→FB+→FG+→F=→0
Null resulting moment regarding point OO
vec F_A xx (A-O)+vec F_B xx( B - O) + vec F_G xx (G-O) = vec 0→FA×(A−O)+→FB×(B−O)+→FG×(G−O)=→0
or equivalently
{(3.5cos 40^@-2.8 cos50^@=f),
(3.5sin 40^@+2.8sin 50^@= m g),
(3.5 cos 40^@-2.8 cos 50^@-2.5 xx 2.8 sin 50^@+x_G m g = 0):}
Solving for f,m,x_G we obtain
f = 0.88 N
m = 4.39/g
x_G = 1.02