Can table2 be the parent of the Task table1? From your description, it seems the machine hours recorded in table2 would be related to the maintenance tasks performed in table1 in a parent >> child relationship. Machine table 2 >>>> has many >>>> Tasks table 1.
Take [Running Hours] in table2 and pass that field along to table 1 as a lookup field. Now, the parent Machine record's [Running Hours] field is present in all tasks related as a child to that table 2 machine record and you can now perform the math in the Task table 1 record.
Have I understood you correctly?