The numbers on the bottom of the diagram are shown to add to 100%. That is,
.. 60% + ?% = 100%
It should not take you long to realize the missing value is 40%.
Then the numbers on the top of the diagram ? and 28 are in the same proportion as 60% and 40%. You can solve this proportion in the usual way.
.. 60/40 = ?/28
.. 28*60/40 = ? = 42
The only remaining missing value is the sum of 42 and 28, which is 70.