Since, the masses are moving with constant velocity, there is no acceleration and hence no external force is acting on them.
Force balance:
For mass m1:
T1=m1g −−−−(i)
Formassm3
T2=μm3g
T2=0.25×4×10
T2=10N
Formassm2:
T1=m2μgsinθ+m2gcosθ+T2
T1=4×0.25×10×35+4×10×45+T2
T1=6+32+10
T1=48N
Puttingin eqn(i)
48=m1×10
m1=4.8kg
Therefore,
The mass m1=4.8 kg and the tension in the horizontal spring T2=10N