When I place mouse over Calculator icon inside the 'Applications' menu it says "Solve simple equations". So I assume this can be done somehow. I tried these expressions.
solve(x=2x+3)
x=2x+3
It says "'solve' is invalid", "'x' is invalid" etc.
You can use NaSC, an application made by Peter A for elementary OS.
More info at NaSC webpage
It's not possible, but there is lot of other tools for that. for exemple, a simple website here.