# tina

posted by
**econ**
.

(100 – 2Px + 1Py) (Px -20)

Now, take the derivative of the above with respect to Px to get the following first order condition :

100- 4 Px + Py +40 = 0

When i try to multiply and then take the derivative of the top part out I keep getting : -1860-4Px-19Py

What am I doing wrong??