點解Will後面可以唔跟動詞? 唔明白結構但知道句子意思。 upon receipt of 點用法? THX?

...the Building Department will upon receipt of a written enquiry provide a determination on the matters
involved in the form of a “letter of assurance” normally within 45 days.
= ...the Building Department will, upon receipt of a written enquiry, provide a determination on the matters
involved in the form of a “letter of assurance” normally within 45 days. (用逗點隔開較清楚)
= ..., upon receipt of a written enquiry, the Building Department will provide a determination on the matters
involved in the form of a “letter of assurance” normally within 45 days. (或移到句前，是標準寫法)

例句:
Upon receipt of a written complaint, the court administrator shall convene the complaint review committee within ten (10) business days to review the complaint.

Upon receipt of a written request, the department shall grant a variance from this rule when the request shows that compliance with this rule would cause unreasonable economic hardship to the requester and that the requested use would not constitute a hazard to people's lives, adjoining property, or the environment.

upon--prep.on
eg:-We will provide(upon receipt of);(a written enquiry).....
(upon receipt of)=an adverb phrase qualifying "will"
when you put a bracket (------) or double commas=(,----,) will make them clear.
eg:-Upon=On receipt of a written enquiry,
the Building Department will provide a determination on the matters involved in the form of a "letter of assurance"=保證書,normally within 45 days.
upon receipt of------eg:-We acted, upon receipt of your claim, and returned all the money owed upon us.
upon,prep:-eg:-The Building decision was based "upon your written enquiry".=was based upon your letter.
eg:-thousands upon thousands of letters are received by the Building Department.