.
Let x and y be amounts invested at 4% and 9%, respectively.
Then you have this system of equations
x + y = 17000, (1) (for total)
0.04*x + 0.09*y = 1380. (2) (for the amount earned)
By solving these equations, you can determine the unknown values x and y.
As a first step you can multiply eqn(1) bu 100 (both sides) to get
x + y = 17000, (1) (for total)
4*x + 9*y = 138000. (2) (for the amount earned)
Next, you can express one of the two unknowns from the eqn(1) and substitute to eqn(2). In this way you will get a single equation
for one unknown, which you can easily solve.
It is how the Substitution method works.
You can find many examples/samples of solved problems on investment in the lesson
- Using systems of equations to solve problems on investment
in this site.
Also, you have this free of charge online textbook in ALGEBRA-I in this site
- ALGEBRA-I - YOUR ONLINE TEXTBOOK.
The referred lessons are the part of this online textbook under the topic "Systems of two linear equations in two unknowns".
Save the link to this online textbook together with its description
Free of charge online textbook in ALGEBRA-I
https://www.algebra.com/algebra/homework/quadratic/lessons/ALGEBRA-I-YOUR-ONLINE-TEXTBOOK.lesson
to your archive and use it when it is needed.