Answer : 3. "350 runs were scored by our team in the Inter-college Cricket Tournament."
Explanation :

The given sentence is in an active voice form, hence we need to convert it into a passive voice form.
Find the subject (Our team) and object (350 runs) of the sentence and exchange their places.
The given sentence is in the simple past tense.
The passive verb form for simple past is: was/were + past participle form of the verb.
So, 'scored' changes to 'were scored'. At last line up the remaining part.
Following these steps, we finally get- 350 runs were scored by our team in the Inter-college Cricket Tournament.