Answer:
75
13-5-7-9-11-13-15=+ + = 30
13-5=8
8-7=1
1-9=-8
-8-11=-19
-19-13= -32
-32-15 =-47
-47=2 =30
-47=2-2=30-2
-47=28
-47+47=28+47
=75
