[xsl] value-of select - then multiply

[j milo taylor <milo@xxxxxxxxxx>]

I am sure i'm missing something pretty simple here:

if I have something like

<xsl:attribute name="translation">
<xsl:value-of select="(position() -1) * 15 "/>
<xsl:text> 3 </xsl:text>
<xsl:value-of select="Work_Year div 10 +0.2"/>
</xsl:attribute>   

how could i do something like this

<xsl:attribute name="translation">
<xsl:value-of select="Work_Location_longitude (position() -1) * 15 
"/><!-- problem here -->
<xsl:text> 3 </xsl:text>
<xsl:value-of select="Work_Year div 10 +0.2"/>
</xsl:attribute>  

I realise this second fragment is incorrect.

I want to get the Work_Location_longitude value, and add an offset 
value to this if there is more than one record with the same 
Work_Location_longitude value.

Any help would be gratefully received.
Best regards
Milo