The mass of the first body is double the mass of the second body.
This all revolves around Newtons 2nd law of motion that states F=m*a.
If we understand that body one has the same force applied but half of the acceleration than body two, we can easily understand that it has to do something with the objects mass. This is because mass and acceleration in newtons 2nd law are inversely proportional. This means if and objects force stays the same, but it’s mass doubles, then the acceleration must be half its original value. And if the acceleration doubles and the force stays constant than the mass must have halved from its original value. It sounds quite complicated but it’s very simple. Hopefully this helps!!!