1. there are two methods to solve this system
I.substition
from the first relation we can deduct
2a-b=4
2a=4+b
a=(4+b)/2
now we substitute a in the second relation
(4+b)/2+b=5
we multiply by 2
4+b+2b=10
3b=6
b=6/3=2
a+2=5
a=3
II.reduction
2a-b=4
a+b=5
we can add the two relations together
2a+a-b+b=4+5
3a=9
a=3
3+b=5
b=2
