Answer: $6,285.71
Step-by-step explanation:
$10,000 to be invested.
The portfolio expected return is a weighted average of the two stocks.
Preferred return = 12.4%

1,240 = 0.15X + 800 - 0.08X
1,240 -800 = 0.07X
0.07X = 440
X = $6,285.71
Invest $6,285.71 in Stock X.