Hello

I've run a panel Fixed Effects model, and i would like to make a graph which detail a part of my result:

```
fe_model <- plm(formula =invest~lag(debt)+lag(I(debt^2))+ lag(I(debt^3))+bcour+gvex+tradeop,data = DataN, model = "within",index = c("country","year"))
``
Coefficients:
Estimate Std. Error t-value Pr(>|t|)
lag(debt) -0.0913478 0.02180357 6.1512 2.517e-09 ***
lag(I(debt^2)) 0.002783274 0.00010127 -5.7105 2.762e-08 ***
lag(I(debt^3)) -0.0000192 0.01620570 1.2259 0.22120 ***
bcour 0.23662511 0.03926279 6.0267 5.018e-09 ***
gvex -0.52866311 0.12588780 -4.1995 3.553e-05 ***
tradeop -3.57865159 1.58891292 -2.2523 0.02505 *
```

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What i want, its to plot (graph) the cubic relation between invest and debt by using each debt coefficients foud in my Fixed Effect model:

plot : invest~lag(debt)+lag(I(debt^2))+ lag(I(debt^3))

Any ideas please?