Three blocks of masses ` m _ 1 , m _ 2 and m_ 3 ` are connected by mass less

Three blocks of masses ` m _ 1 , m _ 2 and m_ 3 ` are connected by mass less string as shown kept on a frictionless table. They are pulled with a force ` T _ 3 = 40 N. ` If ` m _ 1 = 10 kg, m _ 2 = 6 kg and m _ 3 = 4kg`, the tension ` T _ 2 ` will be