Designing a Level Shifter Circuit for 0-5V Output

[-EquinoX-]

Homework Statement

Using the level shifter shown below, design a circuit that will shift a signal from from +/- 25 volts (50 volts P-P) to 0 to 5 volts. Assume R1=R3=100K and R2=R4.
In answer 1 give the value for Vref with 1 decimal point of precision

in answer 2 gie the value for R2=R4 in K ohms.

http://img695.imageshack.us/img695/4536/shifterl.th.jpg

Homework Equations

Vo = (Vin -Vref) R4/(R3+R4) + Vref

The Attempt at a Solution

I am just confused where the R2 takes place... do I just plug and chug

 

[Mindscrape]

Yeah, just plug and chug while maintaining the equalities they tell you to keep. The formula they've made, that you're plugging and chugging into, depends on these equalities.