How do you solve 2x+y=4 and -x+y=1 using the linear combination method?

Is this for solving systems of equations? Or is it for finding y = mx + b form.

Linea combination
combine them to elimiante a vairable
elimiante y's
multily 2nd equation by -1 to get x-y=-1
add that to first one

2x+y=4
1x-y=-1 +
3x+0y=3

3x=3
divide both sides by 3
x=1

sub back

x-y=-1
1-y=-1
minus 1 both sides
-y=-2
times -1
y=2

(x,y)
(1,2)

The correct answer will be d. -4

Well if you have 20 bats you probably want 20 balls? you don’t have enough context to answer the question.