SOLUTION: A person plans to invest four times as much in an account at 4.7​% interest as in an account at 8.4​% annual interest. How much should the person invest in each account

Your equation is 

0.047*(4x) + 0.084x = 408     dollars   (where x is the amount at 8.4%)


To make things easier, multiply both sides by 1000 to get

47*4x + 84x = 408000.


From this point, completing the solution is easy arithmetic.


I leave it to you.