Answer:
18.7 years
Step-by-step explanation:
This is a compound interest problem and the following variables have been given;
Principal = 4000; this is the amount o be invested
APR = 9%; this is the compound interest to be earned
Accumulated amount = 20,000
We are required to determine the duration in years. We apply the compound interest formula;


The next step is to introduce natural logarithms in order to determine n;

The number of years required is thus 18.7 years
The answer & explanation for this question is given in the attachment below.
Answer:
and 
Step-by-step explanation:
Given that
and
, the parametric equations are obtained by algebraic means:
1)
Given
2)
Given
3)
Associative and modulative properties
4)
Existence of multiplicative inverse/Commutative property
5)
Associative property
6)
/ 
7)
Modulative property
8)
Existence of additive inverse
9)
Associative and commutative properties
10)
Distributive property
11)

12)
By 1)
13)
/Result
14)
Compatibility with addition
15)
Compatibility with addition
16)
Associative property
17)
Associative property
18)
Associative and commutative properties/Definition of subtraction/Result
In consequence, the right answer is
and
.