Answer:
In 7.5 years, you will have $21,665.07 - $15,000 = $6,665.07 Interest
Step-by-step explanation:
Let

Step 
Find 

Divide by
numerator and denominator


Step 
Find 

Divide by
numerator and denominator


Step 
Find 


Divide by
numerator and denominator


In this problem
The geometric sequence formula is equal to

For 
therefore
the answer is
the common ratio for the geometric sequence above is 
The answer for the question is: Percentage.
The explanation for this answer is shown below:
By definition, a percentage is a number that is computed on the basis of a whole divided into one hundred parts. Therefore, based on this definition, you can write a percent as percentage (with the symbol %), as a fraction (with a numerator and a denominator) and you can also express it as a decimal, as following:
%
Step 1: Find the slope:

This gives you
, but we need to find b.
To find b, substitute in one (x,y) pair and it doesn't matter which one. I'll go with (4,-2):
![\begin{aligned}-2&=-\dfrac{3}{2}(4)+b\\[0.5em]-2&=-6+b\\[0.5em]4&=b\end{aligned}](https://tex.z-dn.net/?f=%5Cbegin%7Baligned%7D-2%26%3D-%5Cdfrac%7B3%7D%7B2%7D%284%29%2Bb%5C%5C%5B0.5em%5D-2%26%3D-6%2Bb%5C%5C%5B0.5em%5D4%26%3Db%5Cend%7Baligned%7D)
Now take that b-value and plug in into the slope-intercept form:

It's always a good idea to toss in the other x-value from the other point, to make sure it checks out.
Diana's age=21 years
Carmen's age=x years
Andrew's age=2x years
21+x+2x=45
21+3x=45
3x=45-21
3x=24
x=24/3
x=8
2x8=16
Carmen is 8 years old and Andrew is 16 years old. Hoped that helps:)