Answer:
<em>"Seriously, though, he's doing a grand job</em><em>!" </em><em>British TV personality David Frost sarcastically remarked.</em>
Explanation:
When using quotation marks, it's important that all punctuation at the end of the sentences are <em>within</em> the quotation marks.
In the given problem, the exclamation point (!) is outside of the quotation mark, which is wrong. It should be inside the quotation mark like so:
<em>"Seriously, though, he's doing a grand job</em><em>!" </em><em>British TV personality David Frost sarcastically remarked.</em>
<em />
Other than that error, though, the sentence is fine.
Hope this helps!