Hi I have these equations that I wish to know how to reach the variables
for example
${\begin{cases}A=6\\D=A-C\\B=2C\end{cases}}$
All I have is the value of $A$, and $A$ changes from time to time so its not always $6$ it can be $8$, $20$ or anything else.
How can I get the values of each $B$, $C$, and $D$?
Note that, all numbers have to be integer, no floats.