What literary device is , “and his heart was often in his mouth,...”

quite an interesting way to teach topic sentences, because the answer to this question is the best definition of a topic sentence that one can present, it is as if answering the questions taught you how to do it, this is some real teaching, it is terribly well-done.

the topic sentence in this paragraph is:

topic sentences writers stay on track and keep a paragraph from becoming an aimless collection of sentences about an idea.

which incidentally tells you what a topic sentence should be.

the answer is

r ≈5.641

plug in the area of 100 yards into the equation

100=

divide each side by pi

≈ 31.8309=

take the square root of each side to find r

=r

r ≈5.641