Saira invested 1000. part of 8% per annum and the remainder at 9% per annum. after one year, her total interest from these investments was $84. How much did she invest at each rate

х dollars - part of 8% per annum ⇒ 0.08x doll. - income

(1000-x) dollars - part of 8% per annum ⇒ 0.09(1000-x) doll. - income

0.08x - 0.09(1000-x) = 84

0.08x - 90 - 0.09x = 84

0.01x = 6

x = 600

$600 - part of 8% per annum

$400 -  part of 9% per annum