Math 2 equation problem

Question

$25,000 is invested in a fund that has a return of 7​%. How much money is invested in a fund with a 4​% return if the total return on both investments is ​$2310?

Answer 1

.07(25,000) + .04(x) = 2310

Let K = 1000 dollars

.07(25K) + .04x = 2310

multiply both sides by 100

7(25K) + 4x = 231000 = 231K

175K + 4x = 231K

4x = (231-175)K = 56K

x = 56K/4 = 14K = $14,000 invested at 4% interest