Question 810824
investment @ 6%----------x
investment at 8%---------3x

investment @%4 ----------16000-(3x+x)=16000-4x

6%x+8%3x+4%(16000-4x)=934

multiply equation by 100

6x+8*3x+4(16000-4x)=93400

6x+24x+64000-16x=93400

14x=93400-64000

14x=429400
x=29400/14
x=2100 

Investment 4% = 16000-4x
=16000-4*2100
=16000-8400
=7600