What is the value of Va,Vb and Vc by using nodal analysis?
We'd all like to see your work when you post. Please include your prior efforts when you write here.

Often, the problem is as simple as an incorrect sign and the work is otherwise just fine. But it could be more serious. If you don't expose your work, there's no way to know.

Here's how to set up the equations. You can check them against your own work. But what I'm providing here will resolve into the correct answers for you. Let's do the schematic first:







simulate this circuit &ndash; Schematic created using CircuitLab

You'll notice that I swapped the series positions of \$R_3\$ and \$V_1\$. There is no harm in that and it slightly simplifies the equations:

$$\begin{align*}
\frac{V_a}{R_1}+\frac{V_a}{R_2}+I_\text{P}&amp;=\frac{V_b}{R_2}\\\\
\frac{V_b}{R_2}+\frac{V_b}{R_3}+\frac{V_b}{R_4}&amp;=\frac{V_a}{R_2}+\frac{V_1}{R_3}+\frac{V_c}{R_4}\\\\
\frac{V_c}{R_4}+\frac{V_c}{R_5}&amp;=\frac{V_b}{R_4}+I_\text{Q}
\end{align*}$$

I've placed the outflowing currents on the left side and the inflowing currents on the right side. (Clearly, they must be equal to each other.) Very simple to follow and it will solve out correctly.

Compare this with your own work. Chances are, you'll see the problem. (If not, then you probably have still more remedial work ahead of you.)



If you have Sage and sympy installed you can do something along the following lines:

var('r1 r2 r3 r4 r5 va vb vc v1 ip iq')
eq1=Eq(va/r1+va/r2+ip,vb/r2)
eq2=Eq(vb/r2+vb/r3+vb/r4,v1/r3+vc/r4+va/r2)
eq3=Eq(vc/r4+vc/r5,iq+vb/r4)
ans=solve([eq1,eq2,eq3],[va,vb,vc])
for item in ans: ans[item].subs({v1:12,ip:400e-6,iq:8e-3,r1:5e3,r2:5e3,r3:20e3,r4:4e3,r5:4e3})