Janet Invested $26,000, Part At 6% And Part At 3%. If The Total Interest At The End Of The Year Is $1,080, How Much Did She Invest At 6%?

Let x represent the amount invested at 6%. Janet's interest is
$1080 = 6%*x + 3%*($26,000 - x)
$1080 = 3%*x + $780 (use the distributive property, collect terms)
$300 = 3%*x (subtract $780 from both sides)
$300/3% = x (divide both sides by 3%)
$10,000 = x (recognize 3% = .03, evaluate)

The amount invested at 6% is $10,000.