Please help me out!

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

5/6

step-by-step explanation:

if i remember correctly with perpendicular stuff you just take away the negative