Hello, Chokfull!
Edit: Okay, so the "m" is mass.
I got the equation: .
but I don't know how to solve for .
We have: .
. . . . . . . .
Divide by .[1]
Substitute into [1]: .
. . . . . . . . . . . .
. . . . . . . . . . . . . . .
. . . . . . . . . . . . . . .