Thanks to Abel, Michael and David.


<xsl:variable name="numTickets">
  <xsl:choose>
	<xsl:when test="price_type = 56">8</xsl:when>
	<xsl:when test="price_type = 57">4</xsl:when>
        <xsl:otherwise>9</xsl:otherwise>
  </xsl:choose>
</xsl:variable>