Derive an expression for the output current io

Question

Problem:

For the circuit in Figure, assuming all transistors to be identical with β infinite, derive an expression for the output current IO, and show that by selecting

and keeping the current in each junction the same, the current IO will be

1_o = V_cc/2R_E

which is independent of VBE. What must the relationship of RE to R1 and R2 be? For VCC =10 V and VBE
=0.7 V, design the circuit to obtain an output current of 0.5 mA. What is the lowest voltage that can be applied to the collector of Q3: