To determine the value of $x$ in a triangle, more information is typically needed, such as the lengths of the sides or the measures of the angles. The choices given (42, 42, 84, 84) suggest that $x$ might be an angle or part of a calculation related to the triangle's properties.

Given that the sum of the angles in any triangle is $180^\circ$, it is possible that $x$ is related to the angles.

If two of the angles are each $42^\circ$, the third angle, $x$, would be: $x = 180^\circ - 42^\circ - 42^\circ = 96^\circ$ However, since none of the options is $96^\circ$, it's more likely that $x$ could be an angle of $42^\circ$ or $84^\circ$.

To provide an accurate solution, the context or a diagram of the triangle would be necessary.

Do you want further details or have any questions?

Here are some related questions you might find useful:

1. How can the sum of the angles in a triangle help determine missing angles?
2. What are the properties of isosceles triangles regarding angles?
3. How can the exterior angle theorem be applied to find unknown angles in a triangle?
4. What is the relationship between the angles in an equilateral triangle?
5. How do the angles in a right triangle relate to each other?

Tip: Always remember that the sum of the interior angles in any triangle is $180^\circ$.