Answer:

Step-by-step explanation:
Hemi-, demi- and semi- are prefixes which mean <u>half</u>.
When applied to musical notation, each time a prefix is added it means the note's value is <u>halved</u>.
Therefore, if a quaver is one-eighth of a semibreve, then a <u>semiquaver</u> is half of a quaver, which means it's <u>one-sixteenth of a semibreve</u>.

Therefore, a hemisemidemiquaver is one-sixty-fourth of a semibreve.