Now, according to question, m1 moves with constant velocity
⇒a1−a=0⇒a1=a ....(i)
From figure above ,
T−m1g=0⇒T=m1g=1×9.8
⇒T=9.8N .....(ii)
2T=Ma
⇒Ma=19.6 (from (ii)) ...... (iii)
m2g−T=a+a1=29 (from (i))
⇒2a=2×9.8−9.8
⇒a=29.8=4.9m/s2
putting in (iii)
M=4.919.6
⇒M=4kg