30 ° - 60 ° - 90 ° triangle theorem states that:
Base of the triangle is:

The height of the triangle is:

The hypotenuse of the triangle is:

Therefore, we have then that the height is:

From where we conclude that the value of x is:

Thus, the length of the base is:

Finally, the length ZX is:

Substituting values:

Answer:
the length of the lower base, ZX is:

option 3