Why Do Equal Forces Result in Different Accelerations for Two Different Masses?

[boii]

I am needing assistant on my physics homework. I have received the answer of 0.6m/s2 and 0.9ms/2 for the answers but when i check my key that the answer provided it is 3.6m/s2 and when i check over the work they provided it doesn't make sense to me at all. They got the answer of 3.6 by adding the to mass together and dividing by the force. But shouldn't they be different for each since one person weighs more than the other?
two girls, one of mass 40kg and the other mass 60kg, are standing side by side in the middle of a frozen pond.the larger one pushes the smaller one with a force of 360N for 0.10sthe ice is virtually friction less. What is each girls acceleration?

 

[Simon Bridge]

Well, the girl doing the pushing is pushing herself away as well as the other girl.
So they seem to be saying that the force has to accelerate both masses for the same time.
But, like you, I'd have expected that to just mean that both girls get the same change in momentum, not the same average acceleration.