$60.00 + 15%= 69.00. add the 15% to the orinigal Price.
The interest rate is 3.5%.
EXPLANATION
We substitute the given values into the formula;

to obtain

We divide through by 6000 to obtain,

This implies that,

We take the square root of both sides,

This gives us,

Add -1 to both sides of the equation to obtain

Multiply through by 100 to obtain;

%
Divide the number & Multiply