Sven is thinking of tow numbers the sum is 12. the difference is 4

A+b=12
a-b=4
(+)
a+b+a-b=12+4
2a=16
a=8
8-b=4
b=8-4
b=4

Sum means add
difference menad subtract
2 ways to solve,
1, eliminate
x+y=12
x-y=4
so
we can add the 2 equations
x+x+y-y=12+4
2x=16
divide 8
x=8
subsitute
8+y=12
subtract 8
y=4

the other ways is subsiute
x+y=12
x-y=4

x-y=4
add y to both sides
x=4+y
subsitute 4+y for x
4+y+y=12
subtract 4
2y=8
divide 2
y=4
subsitute
x+4=12
subtract 4
x=8

the numbers are 8 and 4