Question: How to assign the solution of 'fsolve' to variables

I'm using fsolve to solve a system of two equations with two unknown variables. Like this,

fsolve({u(b) = z(b-a), u(a) = Zeta1(a-b)}, {a = -.2, b = .2}).

As we know, the solution shows like this:

{b = .2189682330, a = -.1937146254}

I wonder that is there any particular rule for the arrangement of this result? why not {a=..., b=....}

And how can I assign this result to two variables, say aHat and bHat, without being invlved in manually?

Thanks for your help in advance.

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