Hello, darkangel06!

I must assume that you know the Compound Interest Formula.

. .

Sally invests some money at 6%/a compounded annually.

After 5 years, she takes the prinicpal and interest and reinvests it all

. . at 7.2%/a compounded quarterly for 6 more years.

At the end of this time, her investment is worth $14784.56.

How much did Sally originally invest?

Let = her original investment.

She earns annual interest for years.

At the end of five years, she will have:. dollars.

She invests this amount at. quarterly for 24 quarters.

At the end of the six years, she will have:. dollars,

. . which, we are told, will equal

There is our equation!. . . . .

Therefore, Sally originally invested