Tension at the middle of a string of known mass

[natnat_nuts]

Homework Statement

How can i get the tension in the midpoint of a string of mass 2kg that connects two blocks of mass 15kg each if i applied a force 66N to the block on the right to drag the system across a frictionless surface?

Homework Equations

The Attempt at a Solution

 

[rl.bhat]

Hi natnat_nuts, welcome to PF.
what are the relevant equations you have to use to solve this problem?
Show your attempts. Draw the free body diagram of each mass.

 

[natnat_nuts]

my teacher gave us nothing in particular . . . that's why it's difficult. we could use Newton's second law, kinematics, work-kinetic energy theorem etc since we have discussed those already.