Grandma gigi gave leyla a rare purple stone for her sweet 16 birthday. at that time,the stone was worth$245. it has been increasing in value by the same percentage each year, when leyla turned 21, the stone was worth $560.50. if s(t) represents the value in dollars of the stone t years after grandma gigi gave it leyla determine the value of a and r if s(t)=a(r)

This is a compound interest problem, therefore s(t) should be in the form:


where: 
t = time in years
s(t) = the value of your item after t years
a = the initial value of your item
r = rate

Therefore, we already know that a = 245$.

Now, we can calculate r:



     = 1.18

Therefore, the correct answers are a = 245 and r = 1.18

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