I am try do some simple calculations but mic doesnt seem to want to echo it back.

//echo $calc(2 + 2) does not work
//echo $calc(3.1 + 1) works

they both work on //say

try /echo -a $calc(whatever you want to calculate)

In addition to what ethorn said, the reason you're not getting the result you're looking for is because any whole number placed directly after the /echo command is evaluated as a color code.