A function can only have one input to one output. These have more than one output for each input. You can also do the vertical line test, if it touches more than two points at the same time while going horizontally across, it is not a function.
Step-by-steYou can make a new table to add the amounts and copy the pre-existing amounts or just add a new bar, but I guess it will be better if you just do it again.
