Let b>a,
a+b=40 so we can say a=40-b
We are told that b-a=6.5, using a found above in the equation gives us:
b-(40-b)=6.5
b-40+b=6.5
2b-40=6.5
2b=46.5
b=23.25, and since a=40-b
a=40-23.25
a=16.75
So a=16.75 and b=23.25
check...
16.75+23.25=40, 40=40
23.25-16.75=6.5, 6.5=6.5
