PLEASE HELP ME !!

Question

Every hour approximately 16% of the amount of caffeine in the body is metabolized and eliminated (decays). 
a) Write an equation for the amount of caffeine, C, in the body as a function of t, the number of hours since a single cup of coffee was consumed. 
b) Find the time when 20% of the caffeine has been metabolized and eliminated from the body. Give both an exact answer and a decimal answer. Include units. 


In 1997, the average tuition at four-year public universities was $2,360 per year. In 1998, that figure rose to $2,430 per year. 
a) If tuition increased linearly, write a formula for the tuition as a function of years since 1997. Use your function to estimate the tuition in 2006. 
b) If tuition increased exponentially, write a formula for the tuition as a function of years since 1997. Use your function to estimate the tuition in 2006. Note: The average tuition in 2006 was actually $4,102.

Answer 1

a)

Recall the formula

Where

y = ending amount

b = growth or decay factor

a = initial amount

x = time

a) Decay factor b is always 0 < b < 1

b  = 16% = 16/100 = 0.16

a  = 1

Write the equation to the decay value of the caffeine

b) 20% of caffeine eliminate from the body

Remaining caffeine = 80%

Apply log on each side.