What is a thesis statement?
an implied idea that will be developed throughout a paragraph
the audience and purpose of a composition
a generalization about the evidence you are going to present
a sentence that sums up the main idea of your composition

The last one

Explanation:

a sentence that sums up the main idea of your composition

for this case, we must find the number of deaths per day of the year 2015, in automobile accidents, knowing that 32,400 people died.

knowing that the year 2015 had 365 days we have the following division:

where "x" represents the number of deaths per day.

rounding off we have:

approximately, 89 people per day died in 2015

answer:

89 people per day