HELP HELP HELP What is the explicit rule for the arithmetic sequence?

20.5, 18, 15.5, 13, 10.5, ...

an=23+2.5n

an=20.5−2.5n

an=20.5+2.5n

an=23−2.5n

Kayla and alberto are selling fruit for a school fundraiser. customers can buy small boxes of grapefruit and large boxes of grapefruit. kayla sold 3 small boxes of grapefruit and 1 large box of grapefruit for a total of $65. alberto sold 1 small box of grapefruit and 1 large box of grapefruit for a total of $55. what is the cost each of one small box of grapefruit and one large box of grapefruit?

(60 points) explain this in detail

Aculture started with 2,000 bacteria. after 8 hours, it grew to 2,400 bacteria. predict how many bacteria will be present after 19 hours . round your answer to the nearest whole number. p=ae^kt