Gimana caranya mohon bantuannya

Anggap tegangan tali antara benda 3 & 2 T1, antara benda 2 & 1 namanya T2

Tinjau sistem
∑F = m total × a
20 = 5 a
a = 4

Tinjau benda 1
∑F = m1 a
20 - T2 = 2,5 × 4
T2 = 10 N

Tinjau benda 3
∑F = m3 a
T1 = 1 × 4
T1 = 4 N