Three blocks of masses m_1, m_2 and m_3 are connected to a massless string on a frictionless table as shown in the figure. They are pulled with a force F = 40 N. If m_1 = 10 kg, m_2 = 6 kg, and m_3 = 4 kg, then tension T_2 will be ________.
1) 10 N
2) 20 N
3) 32 N
4) 40 N