Current-Steering Circuit
The base and collector of Q1 and Q2 are tied together.

$$V_{CC}+V_{EE}-V_{BE1}-V_{BE2}$$

is simply the voltage across R.

Edit to include comment discussion:
The voltage across R is just the total voltage drop in the current path, (Vcc + Vee) minus the other drops (Vbe1 + Vbe2). You are left with the drop across R, or

$$(V_{CC} + V_{EE}) - (V_{BE1}+V_{BE2})$$