problem is "The circuit of Fig. 5-7 has a current of 2.5mA (milli-amps). Find the following quantities...

"Given" R1 = 3.3kΩ R2 = ? R3 = 5.6kΩ I = 2.5(mA) E = 45V

My teacher has taught us how to do Rτ and ƩV. But he has yet to show us how to find a resistor when one is missing... either that or its so obvious that i am not grasping it.... Help please? All i need to do is find R2 and the rest i can solve on my own.

A) The total resistance of the curcuit.

B) The value of the unknown resistance (R2)

C and D i am choosing not to put on here because i know how to do them.