How do I solve this? Please show work, thank you.

Answer:
a x sqrt(7) - 49sqrt(x)
Step-by-step explanation:
sqrt(7x) [ sqrt(x) - 7sqrt(7)]
Distribute
sqrt(7x) *sqrt(x) - sqrt(7x)*7sqrt(7)
We know that sqrt(a) sqrt(b)= sqrt(ab)
sqrt(7x^2) - 7sqrt(7^2 *x)
Now lets separate out the perfect squares
sqrt(7) *sqrt(x^2) - 7sqrt(7^2)*sqrt(x)
x sqrt(7) - 7*7sqrt(x)
x sqrt(7) - 49sqrt(x)
Answer:
√(7·x)·(√x - 7·√7)
= √(7·x)·√x - √(7·x)·7·√7
= √7·√x·√x - √7·√x·7·√7
= √7·x - 49·√x
= x·√7 - 49·√x
So answer a is correct.