The amount on interest he earned is $5116.8
Step-by-step explanation:
Given,
Principal(P) = $16400
Rate of interest(R) = 3.9%
Time(T) = 8 years
To find the interest
Formula
Simple interest = 
Hence,
The interest =$ 
= $5116.80
Associativ property
a(bc)=(ab)c
ability to move parenthaseese around
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-6/7 < -6.7
i hope this helps