hi, attached are my working. Pls verify if my answer were correct. first convert norton part to thevenin. thus the current-ctrl voltage source is 70i & 20Ω in series with the circuit. to compute V, -10 + 10i + 20i - 70i=0 i= -0.25A i(20)-(70i)= -5+17.5= 12.5V =V next to compute I short the ab terminal, I= i - 3.5i v=0, (-10+v)/10 = -i i= 1 thus, I= 1 - 3.5 = -2.5A hence R= 12.5/-2.5 = -5Ω i m wondering if i got them right.