We need to use the formula for simple interest which is 
I= prt
Where I is the amount of money you earned or pay in interest
 p is the principal, the amount you deposited or borrowed
 r is the interest rate expressed as a decimal
 t is time in terms of years
In this problem, I= 1,680
 p= 3000
 t= 8
 '. r is what we are looking for.
Substituting the numbers into the simple interest formula, we get
I=. p r t
1,680=(3000)(r)(8). Multiplying
1,680= 24,000r Divide both sides by 24,000
 0.07= r
So, the percentage is (0.07)(100)= 7%...