Steven made two investments for a total amount of $1,680. One investment is at 7% and the other at 4%. The annual simple interest from the 4% investment is $20.80 less than the interest from the 7% investment, How much money was invested at 4%?
( 1680 - x) (.07) = ( x) (.04) + 20.80
117.6 - .07x = .04 x + 20.80
117.6 - 20.80 = .11x
96.8 = .11x
96.8 / .11 = x = $880 at 4%
