I'm pretty sure you mean k² + 16k + 64. If we simplified k² + 16 + 64 to k² + 80, that expression wouldn't be factorable. This is how k² + 16k + 64 would be factored:
k² + 16k + 64
(k + 8)(k + 8) or (k + 8)²
To test if this is correct factoring, simply multiply the terms back together and see if you end up with your original expression. Use FOIL -- First, Outside, Inside, Last -- multiplication (see attached picture):
(k + 8)(k + 8)
k² + 8k + 8k + 64
k² + 16k + 64
Check! The factored form of the expression k² + 16k + 64 is (k + 8)(k + 8) or (k + 8)².