for simple interest we have the following equation:

interest = principal * rate * time

an increase from 4850 to 8000 represents how much interest:

8000-4850 = 3150

for our problem we now know the following values:

interest = 3150

principal = 4850

rate = 0.076

let 't' represent the time of investment in years:

3150 = 4850 * 0.076 *t

solving for 't' we have:

t = 15750/1843

t = 8.5458

Cynthia will need to leave the money invested for approximately 8.6 years