It isn't possible to answer that question without further information. Specifically are each of the three tests equally weighted, or, for example, does the third test carry twice the weight (double the marks) of the first one, (having twice as many questions) ?
If the three tests are equally weighted, you can think of them as making up the remaining 80 marks out of a 100 left when the practical mark has been removed, and so worth 80/3 marks each. In that case the overall mark would be
(80% of 80/3) + (70% of 80/3) + (65% of 80/3) + (60% of 20)
which comes to about 69.33 out of 100 i.e. 69.33%.
If the tests are not equally weighted then you need to substitute other values (adding up to 80) for the three 80/3's.
There should be a module description form (or whatever the school or college choose to call it) defining how the module is to be assessed and that should contain the relevant information.