Question 243625
.06x+.04(12,000-x)<=640
.06x+480-.04x<=640
.02x<=640-480
.02x<=160
x<=160/.02
x=$8,000 amount invested @ 6%.
12,000-8,000=$4,000 amount invested @ 4%
Proof:
.06*8,000+.04*4,000<=640
480+160<=640
640<=640