The forces f 1, f 2, f n acting at the same point p are said to be in equilibrium if the resultant force is zero, that is, if f 1 + f 2 + + f n = 0.
f 1 = i + j, f 2 = i – j, f 3 = 9 i + 2 j
find the additional force required for the forces to be in equilibrium p.

F1 =<1, 1> in this case, consider F1 as u = <u1,u2>=<1,1>
F2= <1,-1>
F2 as v = <v1,v2>= <1,-1>
F3= <9,2>
F3 as w =<w1,w2>=<9,2>
F4 = <x, y> such that x + u1+v1+w1 =0
or x = -u1-v1-w1
so F4 = <11,2>
x + u1+ v1 + w1 =0 or x = - u1 -v1-w1 = -1-1-9 =-11
so its -11,-2
hope this helps

The speed was not exceeded so it was slow

Inner peace.. jk it's  a stable electron configuration