1020I1 + 550I3 + 470I5 = -10
1460I2 – 420I3 -600I4 =-5
320I1 – 420I2 + 1200I3 =0
-820I2 + 1250I4 – 100I5 = -15
470I1 – 100I4 + 770I5 = 0