How do I solve this problem?

It should be x^4/7 (the first option). When you multiply square roots, you can convert them into x to the root of whatever the numbers are. An example would be the square root of x. You can convert that to x^1/2. The root on the outside is the denominator and the exponent on the inside is the numerator. For this one, you'd convert it to x^1/7. Then, you'd add all of the exponents up. 1/7 + 1/7 + 1/7 + 1/7 = 4/7. If you wanted to convert it back to a root form, it'd be ^7√x^4, but since there's no option for that, it'd be x^4/7