How do I find the solution to this answer

Trina divided her $25,000 inheritance between two investments,one paying 9% and the other paying 12% simple interest. Her total income on the interest alone was $2,550. How much did she invest at 9% ?

Assuming interest for 1 year
0.09x+0.12(25000-x) = 2550
-0.03x = -450
x = $15,000