Which of the following sentences is grammatically correct?

i was late to dinner there was a traffic jam.
i was late to dinner, there was a traffic jam.
i was late to dinner; there was a traffic jam.
i was late to dinner for the traffic jam.

Read this student's rough draft. i know it doesn't sound like much, but am psyched about the school fundraiser this spring. we are sponsoring a slam-dunk contest (on an eight-foot rim) for local middle schoolers. we're charging an entry fee for participants that will cover our costs, and we’ll charge admission at the door! three dollars per person—ka-ching! six of my neighbors have already said they are coming. i mean, who wouldn't come? participants will wear their school jerseys, and all their friends will come to cheer! which concluding sentence best reflects the writer's voice? the contest will take place in the liberty middle school gym, and the maximum capacity is 250 spectators. the contest promises to enrich our community as a variety of schools unite to support our fundraising effort. it will be sweet, because the band is providing music in the stands, and the dance squad is performing. students’ enthusiasm for this endeavor has blossomed, and it will reach full flower as the contest approaches