Both Kyla and Tia will be in their zone. Even if they dicrease their heart rates by 20 beats per minute from 175 beats per minute. 155 beats per minute still falls under kyla's target heart rate zone and Tia's target heart rate zone.
That would be Anatomical Root
My answer to the question is option A and B.
I would be a physicist or way better application specialist without additional training
