let = tension in the string between the surface mass and the hanging mass.

= tension in the string between the hanging mass.

I'll assume the 4kg mass is above the 6 kg mass.

net force equation for the surface mass (10 kg) ...

net force equation for the 4 kg mass ...

net force equation for the 6 kg mass ...

solve the system of equations for , , and " " ... you should get , Newtons, and Newtons.