1) I = 2 amps

2) V = -50 volts

3) I = -5 amps

4) i1 = 1 amp, i2 = 1 amp

5) Vx = 17.5 volts

6) i1 = -5 amps, i2 = 3.333 amps

7)
Node 1: 9 * V1 + (-5) * V2 + 0 * V3 = -70

Node 2: 5 * V1 + (-17) * v2 + 4 * v3 = -70

Node 3: 0 * v1 + 2 * v2 + (-3) * v3 = -20

(note that there are other correct numerical coefficient values that are simply scalar multiples of these coefficients).