How do you write 7,870 in scientific notations ?

Which situation can be modeled by the inequality 5 + 10w ≥ 45? a. you start with $5 and save $10 a week until you have at least $45. b.you start with 5 baseball cards and purchase 10 cards every week until you have at most 45 cards. c.you start with 5 water bottles and purchases cases of 10 water bottles each until you have a total of 45 water bottles. d.you spend $5 plus $10 per week until you have less than $45.

Could somebody me with this radical simplification?

Rectangle bcde is similar to rectangle vwxy. what is the length of side vy? a) 1 7 b) 2 7 c) 3 7 d) 4 7