how many years will it atke 6000 invested at 8 interest to e

how many years will it atke $6000 invested at 8% interest to earn $1680

Assuming this is simple interest:
I = Prt (interest = principle x interest rate x time)
In your question
I = 1680
P = 6000
r = 0.08
t = ?
I = Prt
1680 = (6000)(0.08)(t)
1680 = 480t
t = 1680/480
t = 3.5 years