Excel doesn't have a built in "algebraic manipulator." If you set the spreadsheet up right, you should be able to get Solver to "solve backwards" for A and X. But, if time is really that important, you'll want to work through the algebra to get explicit functions for X and A as functions of B and Y: (In the following equations, I've absorbed the 100's into B and Y)
C=A/B, Z=XY
A/B-X=10 eqn(1)
XY-A=10 eqn(2)

At this point, there are two equations in 2 unknowns (A, X). Use the method of elimination as explained here: http://www.analyzemath.com/Tutorial-...Equations.html to eliminate A or X

AY/B-XY=10Y
-A+XY=10

add together
AY/B-A=10Y+10
A=(10Y+10)/(Y/B-1)

Having solved for A, it should be simple to get X from eqn 1 or 2.