math question - need help

Question

After graduating from college, Julie decided she wanted to start investing money. She had a total of $8,000 to invest into three different accounts: a mutual fund paying 7.5% interest, a stock paying 10% interest, and a money market paying 2.25% interest. Julie's total interest she made in one year was $452.50. Additionally, the amount she invested in the mutual fund and stock together was equal to the amount she invested in the money market. 

How much did Julie invest into the mutual fund? 

How much did Julie invest into the stock? 

How much did Julie invest into the money market?

Answer 1

f +s +m = 8,000

.07f +.10s +.0225m = 452.50

f+s = m

3 equations 3 unknowns

solve by substitution/elimination or matrix algebra

f+s+m =8000

m+m = 2m = 8000

f+s=m = 4000

m= $4000 invested in money market

that gives x=$1250 for funds

and y= $2750 for stocks

.07(1250) + .1(2750) + (.0225)4,000

= 87.50+ 275 +90

= 177.5 +275

= 452.50