Two planets, A and B, are at rest with respect to each other, a distance L apart, with synchronized clocks. A spaceship flies at speed v past planet A and synchronizes its clock with A’s (they both set their clocks to zero). It then flies past planet B and compares its clock to B’s. We know that when the spaceship reaches B, B’s clock will simply read L/v. And the spaceship’s clock will read L/γv, since it runs slow by a factor of γ, compared to the planets’ clocks.
How would someone on the spaceship quantitatively explain to you why B’s clock reads L/v (which is more than its own L/γv), considering that the spaceship sees B’s clock running slow?