System of equations question

Question

A bank is paying 6% annual interest on 1 year certificates, and treasury notes are paying 3% annual interest. An investor wishes to receive $2400 interest at the end of 1 year by investing $60,000. How much was invested at each rate?

Answer 1

X+Y = 60000

0.06X + 0.03Y = 2400

0.06 ( 60000 - y) + 0.03Y = 2400

3600 - 0.06y + 0.03y = 2400

- 0.03y = -1200

y=40000

20000 in certificates , 40000 in treasury notes