Calculating a string?

[lalabored]

I need a function that is able to evaluate a string.  For example, I have $var = "3+4*5", is there a function that can be like function($var) = answer?? It has to be able to recognize that 4*5 is done first.

[The Little Guy]

like this?

 

eval(str_replace('"','','$var = "3+4*5";'));

echo $var;