How do I calculate "to the power of" on HP 10bii+ ?

SOURCE: CPT button on HP Calculator

You don't need a cpt button on Hp 10ii calculator.You can just press the function button that you want to apply without pressing cpt first.

SOURCE: what is the LOG function on the HP 10bII

The 10bII does not have a key for the common logarithm function. You can use the natural logarithm function (LN, the shifted function of the 2 key) to compute the common logarithm of a number using the relationship
log(x) = ln(x)/ln(10)

In words, calculate the natural log of the value and divide it by the natural log of ten.

SOURCE: I have a HP 10bII

You can use the I/YR key on the top row to enter/calculate the interest rate.

We can't tell whether your numbers are correct or not without seeing them. Could you post the problem?