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Opamp circuit question

1. The problem statement, all variables and given/known data
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http://www.chegg.com/homework-help/questions-and-answers/ideal-opamp-find-v0-terms-vs-need-help-solving-vp-firstly-understanding-parts-q8278769
2. Relevant equations

I am having difficulties with this problem. It asks to find vo in terms of vs. For the gain, I got an equation of Vn/10 + (Vn-vo)/40 = 0, so vo=5Vn. Since the op amp is ideal, vn=vp. Now for Vp is where i am having trouble. I have an equation of [48/60]vs - [48/60]4V=vp. But i am not sure if this right, I am not getting the correct answer. Help!
3. The attempt at a solution
 

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rude man

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1. Label all resistors R1 - R4 and the 5V source V. Don't substitute with numbers until your calculations are done. I can't follow your numbers.
2. Compute vp, then vp=vn as you say, that gives you the current thru the feedback resistor and the output follows immediately.
 

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