I was dumbfound when Jimmy cheated yesterday
The math problem left him dumbfounded.
Yes.
dumbfounded
The enemy is now at the gate.
The mythical hydra had seven heads. There are seven days in one week.
There are seven continents in the world
The participles of the verb "to dumbfound" are dumbfounding and dumbfounded. The choice would depend on whether the noun is performing the action or responding to it, with dumbfoundedthe more common.
Each word in this sentence has only one syllable. There are seven words, so there are seven syllables in the sentence.
We can't answer that accurately without knowing the sentence.
The teachers' meeting is scheduled for seven.
There is a box that I'll deliver.
The cake had seven different layers.