Using a value from table 2 to makes a calculation

Asked before now with an example.

In PowerBI I like to make a calculation with numbers from 2 tables.

1. sum the hours of a person from table 1 (John has 30 + 5 = 35 hours)

2. divide this sum with the number in table 2 on the record whichs has John's name, in this exemple 35/5.

Powerbi gives an error that says values from table 2 has to be a sum, max or minimum value (aggregation)

How can I use the value which is found in John's record in table 2?