If $5700 is invested at a 5% annual simple interest, how much should be invested at 9% annual simple interest so that the total yearly income from both investments is $1077?

Firstly we need to find out how much is 5% from $5700:

5700 * 5% =
= 5700 * 5/100 =
= 57 * 5 =
= 285

$1077 - $285 = $792

So now we need to find out how much should be invested at 9% annual simple interest to earn $792.

792 = 9% from x
792 = 9/100 x            / * 100 (both sides)
79200 = 9x                / ÷ 9 (both sides)
x = 8800

When investing $5700 at 5% annual simple interest, also $8800 at 9% annual simple interest should be invested to have the total yearly income of $1077.

25% increaseplus i think decrease i only know increase: ((