I figured it out. I had to add a COM reference to Microsoft Script control like so:
Then I just declare my new variable as a Script Control.
Dim ScriptControl1 As New MSScriptControl.ScriptControl()
ScriptControl1.Eval("(10+1.5)") ' Returns 11.5
Note*
Make sure your Target CPU is at x86! I would receive a COMException if i had it set to Any CPU.