Answer
The tension in the rope is $88N$.
Work Step by Step
1) First, let's look at the whole system of 2 boxes
- Each of the box has mass $m$, so mass of the system $M=2m$
- The pulling force that acts on the system $P=176N$
- Total kinetic friction acting on 2 boxes: $\sum f_k=\mu_k\sum F_N=\mu_k(2mg)=2\mu_kmg$
Since the system is pulled at a constant velocity, it has no acceleration, so $$\sum f_k=P$$ $$2\mu_kmg=176N$$ $$\mu_kmg=88N$$
2) Now, let's examine the box behind
It is pulled by tension $T$, whose motion is opposed by $f_k=\mu_kmg$
This box also has no acceleration, so $$T=f_k=\mu_kmg=88N$$
