Based on this graph, how has automobile usage changed?

It has decreased by about 20% among young people.
It has increased by about 20% among young people.
It has decreased by about 40% among young people.
It has increased by about 40% among young people.

it has decreased about 20%

Explanation:

it is obviously  over -20% but is still closer to -20%  than -40%

i confess that there are several parts of this constitution which i do not at present approve, but i am not sure i shall never approve them: for having lived long, i have experienced many instances of being obliged by better information or fuller consideration, to change opinions even on important subjects, which i once thought right, but found to be otherwise. it is therefore that the older i grow, the more apt i am to doubt my own judgment, and to pay more respect to the judgment of others.