there are 40 compact cars, 4 of 10 each.
there are 30 mid-size, 3 of 10 each.
and there are 20 trucks,
however, in the graph, they all seem to have the same start point and end point, and the mid-size are elongated more than the compacts, and the trucks are much larger than the others above it, almost suggesting the amounts for all are equal somehow for that period.
the amounts must correlate horizontally as they're laid, thus the compacts should be longer than the rest, the mid-size behind it and the trucks half-way of the compacts.