HELP! my prelude wont start

[sleepercrx90]

my 88 prelude si(b20a5) ran fine this morning. i drove it into town and went inside a store, when i came out to start it it wouldnt start. it turns over fine, but if u crank on it for about 5 seconds it backfires and sounds like a gunshot.

i think it would be spark or fuel, but i dont know for sure. any help, please