How do I work with smarty variables in Oxid

Hi,
I am trying to do some arithmetic in smarty as I know it from another project but it does not seem to work here.
What is wrong in this code?

[{assign var="tmpjvl" value=$product->getMinPrice()}]
[{assign var="tmpjvl2" value="'(1.2 * $tmpjvl)'"}]
[{oxprice price=$tmpjvl2 currency=$oView->getActCurrency()}]

the line in the middle breaks the code.

I want to present the netprice - the price and the vat.

Kind regards,
Jan