Question

x+y=4 solving by substition
x-y=8.8

Answer 1

Add the two equations together: 2x=12.8 => x=6.4
6.4+y=4=>y=-2.4
6.4-(-2.4)=>8.8 as required

Answer 2

x + y = 4
x= 4- y........(i)
x - y = 8.8.....(ii)
Substituting i in ii
4 - y - y = 8.8
4 - 2y = 8.8.......... -2y = 8.8 - 4
-2y = 4.8 devide both sides by -2
y= -2.4
then substitute y in i......... x = 4 - -2.4
x= 6.4
can confirm this with equation i 6.4 + (- 2.4)
6.4 - 2.4 = 4