XSLT adding information in columns to HTML table instead of rows

I've been given this XML code and I'm supposed to transform that into a traditional HTML timetable with day names on the top row and times on the right. It becomes so tricky for me when I try to write the rows for each time. By the way, don't consider the attribute priority ¿Could anyone please help me with this? Thanks in advance.

<?xml version="1.0" encoding="ISO-8859-1"?>
<timetable>
   <day>
      <numday>1</numday>
      <task priority="medium">
          <time-sta>12</time-sta>
          <time-end>14</time-end>
          <name>Tutorías</name>
      </task>
   </day>
   <day>
       <numday>2</numday>
       <task priority="high">
           <time-sta>12</time-sta>
           <time-end>14</time-end>
           <name>Autómatas</name>
       </task>
   </day>
   <day>
       <numday>4</numday>
       <task priority="high">
           <time-sta>9</time-sta>
           <time-end>11</time-end>
           <name>Procesadores de lenguajes</name>
       </task>
       <task>
           <time-sta>16</time-sta>
           <time-end>17</time-end>
           <name>Matemática Discreta </name>
       </task>
   </day>
   <day>
       <numday>3</numday>
       <task priority="high">
           <time-sta>9</time-sta>
           <time-end>11</time-end>
           <name>Procesadores de lenguajes</name>
       </task>
   </day>
   <day>
       <numday>5</numday>
       <task priority="low">
           <time-sta>17</time-sta>
           <time-end>18</time-end>
           <name>Ver la tele</name>
       </task>
   </day>
</timetable>