114-these sentences are not correct. They should read “there was a letter which was written” and “there were people working hard” the passive form expresses the action in the statement, therefore “working hard” modifies “people” and “which was written” modifies “letter” example: she was walking home when they met.
115-the sentences are not correct; “the differences is that the words “which/that” emphasis. Example: the girl with the red hat has two kittens.
116-the first sentence is not correct; the second shows that the person has in their possession a book. “There is a person with a book”. Example: we cheered with loud voices.
117-the first sentence is correct, however the preposition “with a car” modifies the object “I need to go” so that we can have “I have to go with a car” prepositions modify adverbs, adjectives and nouns that they follow right after. Example: he has a fish with red gills.
118-the sentence means that the one will find the book and the pen together.
Example: I am going with her to the market.