Answer:
2√42 + 7√2 - 6 - √21
Explanation:
Use the FOIL method: first terms, outer terms, inner terms, last terms:
√[14·12] + √[14·7] - √36 - √21
This simplifies to: √[3·4·14} + √98 - 6 - √21, or
2√42 + 7√2 - 6 - √21
This matches the first answer choice.