The diagram is very helpful. I've uploaded it below.
Given
AB = x
AC = 2x
MO = 5
MO = 1/2 AC
Argument
MO = 1/2 AC from the transformation
5 = 1/2 AC MO is given as 5. Multiply by 2
5*2 = AC
10 = AC
AC = 2*AB
AC = 2* x
10 = 2 * x Divide by 2
x = 5
AB = 5.
