The expression $-6\sqrt{7} + 2\sqrt{7}$ involves like terms, as both terms contain $\sqrt{7}$. You can factor out $\sqrt{7}$ and combine the coefficients:

$(-6 + 2)\sqrt{7} = -4\sqrt{7}$

So, the simplified expression is:

$-4\sqrt{7}$

Would you like more details on how this simplification works, or do you have any other questions?

Here are 5 related questions you might find helpful:

1. How do you simplify expressions with square roots?
2. What is the difference between like and unlike terms in algebraic expressions?
3. How can you combine terms with radicals?
4. What happens if you have different radicals in an expression?
5. How do you rationalize a denominator with square roots?

Tip: Always look for like terms, even when dealing with square roots, to simplify expressions more easily!