Given:
To round off to the nearest tenth of the given numbers and identify the underestimate term.
Consider the first term.

Consider the second term.

Consider the third term.

Consider the fourth term.

Consider the fifth term.

Thus, the obtained results are 67.1, 20.4, 86.6, 99.5, 41.5.
By comparing the results the underestimate term will be 20.4
Hence, option (b) is the correct answer.