0.03. Multiple ways are again possible, I would go for `ifelse` statement.
Here's what the resulting [output](doc/tasks/05_out.pdf) plot should look
like.
6. Add a `Fit` variable to your dataframe for fitness. OD is a fine measure and much can be learned staring at growth curves [[ref](https://www.annualreviews.org/doi/abs/10.1146/annurev.mi.03.100149.002103)].
But we're interested in the effect of the drug i.e. how much
better/worse do bacteria grow upon treatment. To that end, use the same
grouping as for OD (on each day, on each plate, in each timepoint) and
derive fitness as `OD = OD/OD[uM == 0]`. Please also constrain `Fit` to
1.1 (there's no real need for constraining fitness, it is just for making
plots look nicer). Here's what [output](doc/tasks/06_out.pdf) plot should look like if you now plot everything exactly as in the step above, except having `Fit` on y-axis.
