Interest question

Question

Laura borrowed a total of $21,000 from two different banks to start a business One Bank charge the equivalent of 3% simple interest and the other charge 4.5% interest if the total interest after 3 years was 2070 dollars determine the amount borrowed from each Bank

Answer 1

a + b = 21,000

3(0.03a + 0.045b) = 2070

 

a = 21,000 - b

0.03a + 0.045b = 690

 

0.03(21,000 - b) + 0.045b = 690

630 - 0.03b + 0.045b = 690

0.015b = 60

b = 4000

 

a = 21,000 - 4000

a = 17,000