What is (4.2×10^9) in scientific notation

In the film, zeke the zombie slayer versus the zombies from space, zeke slayed 140 zombies. in the sequel, zeke the zombie slayer versus the zombies from space, part 2, he slayed 5% more zombies. how many zombies were slain by zeke in the sequel?

Quick translate "x is 12 units from 20" into an equation. what are the values of x being described? if you can answer any of my other questions that'd be great too

Trent wants to buy 2 packs of trading cards for 3 dollars each. the trading card packs that trent normally buys tend to come in packs of 6, 10, 12, or 15 cards. after selecting 2 packs, trent found that the first pack of cards cost 25 cents per card, and the second pack cost 30 cents per card. trent uses this information to write the equations below in order to compare c, the number of cards in each pack.