we know that
The formula of simple interest is equal to

In this problem
we have
I=$170
P=$8,500
r=4%=4/100=0.04
t=?
substitute given values in the formula

therefore
0.5 years=6 months
<h2>The answer is 6 months</h2>
1, -1 !!! i hope this helps (also download mathpapa :D )
ANSWER

EXPLANATION
The given expression is

We factor to get,

This implies that,

We factor further to obtain,

or