Answer:
1. 
2. not completely sure but i think its 
3.x
=
2
i
√
5
,
−
2
i
√
5
4.x
=
−
9
±
√
73
/2
5. Im not sure...
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Ni : Zn: Cu = 7:2:9 =7x : 2x : 9x
7x+2x+9x = 3.8
18x=3.8
x=3.8/18=1.9/9≈0.21
Ni: 7x=7*0.21=1.47 ≈1.5 kg
Zn: 2x=2*0.21=0.42≈0.4 kg
Cu: 9x=9*0.21=1.89 ≈1.9 kg
Check 1.5+0.4+1.9 =3.8 True
It would be 11 if I’m reading this right