Answer:
12 years
Step-by-step explanation:
Simple interest formula:

where
I = interest,
P = principal,
r = rate (as decimal),
t = time
In your case,
P = $616
I = $1,007.78 - $616 = $391.78
r = 0.053
t - unknown, so

bearing in mind that a diagonal line from the center of a square will give us an isosceles triangle, Check the picture below.