if r1 has value of 600 and r2=r3=r4=400 ohms. supply voltage is 10v. im getting the wrong answer and do not know how. im using [(R4R2 - R3R1) / (R1+R4)(R2+R3)] * VS i get an answer of [160000 - 240000 / (1000)(800)] * 10 = [-80000 / 80000] * 10 = -1ohm but this is the incorrect answer. where am i going wrong?