Answer:
The amount invested in the account that paid 8% was $18,000
The amount invested in the account that paid 10% was $6,000
The amount invested in the account that paid 12% was $26,000
Explanation:
Let
3x -----> the amount invested in the account that paid 8%
x -----> the amount invested in the account that paid 10%
$50,000-4x ----> the amount invested in the account that paid 12%
in this problem we have

we know that

Solve for x






therefore
The amount invested in the account that paid 8% was $18,000
The amount invested in the account that paid 10% was $6,000
The amount invested in the account that paid 12% was $26,000