The information given:
a+b=8 (the sum of two numbers is 8)
b=a-6 (one number is 6 less than the other)
Since we have two equations and two variables, we can substitue one equation on the other:
a+(a-6)=8
a+a-6=8
2a-6=8
2a=8+6
a=14/2
a=7
Since we have a, now we substitute a in the equation:
7+b=8
b=8-7
b=1