Answer:
They are located in the equatorial positions
Step-by-step explanation:
To know this, we need to draw the chair conformation of the cyclohexane.
As you can see in picture 1, we have a cyclohexane with the two methyl in position 1 and 3, both of them with a wedge bond meaning they are in cis position.
The next structure is the chair conformation of the 1,3-dimethylcyclohexane. Facing in cis position they could be either in axial positions (Facing upward) or equatorial positions (Facing to the sides).
Now both of them are in cis position, however, one of them is the most stable conformation. This one would be the equatorial positions. Why is that structure more stable than the axial positions? basically, because when you have a cyclohexane with radicals in position 1 and 3, you can have the 1,3-diaxial interactions which is an interation that is usually repulsive between those substituent. Therefore, this repulsion of the methyls, it's similar to steric hindrance and make this conformation being less stable than the conformation in the equatorial positions, because you can see there are no interaction there and no steric hindrance. Therefore the methyl groups should be located in the equatorial positions to do the most stable conformation. See picture attached.