According to the figure given in question, all 3Ω resistances are in parallel combination. So, their equivalent resistance is
1
Rparallel
=
1
3
+
1
3
+
1
3
1
Rparallel
=
3
3
⇒Rparallel =1kΩ
5mathrmkOmega and 1mathrmkOmega resistance are in series to the equivalent of all 3Omega resistances. ∴Rnet =5+1+Rparallel ...(i) ⇒Rnet =(5+1+1)kΩ=7kΩ=7×103Ω ∴ The value of electric current flowing through 5kΩ resistor will be I=
V
Rnet
=
21
7×103
=3×10−3A =3mA Comparing with the given value in the question i.e., xmA, the value of x=3.