If caffeine reduces by about 10% per hour, how many hours h does it take for the amount of caffeine in a body to
reduce by half (round up to the next hour)?

7 hours

Step-by-step explanation:

Since, the final amount of caffeine formula would be,

Where,

P = Initial value,

r = rate per period,

t = number of periods,

Here, r = 10% = 0.10, t = h, A =

Taking log both sides,

Hence, after 7 hours the amount of caffeine in a body to  reduce by half.

here

step-by-step explanation:

8(-10x+3.5y-7)

8×-10x + 8×3.5y + 8×-7

-80x + 28y - 56

therefore

-80x+28y-56 is the correct answer