Slove the system by substitution
x+y+z=4
x+y-z=4 , 3x+3y+z=12
step by step
this is algebra 2

I would use eliminateion

look at first equation and second

x+y+z=4 and
x+y-z=4
notice
x+y+z=4=x+y-z
or
x+y+z=x+y-z
minus (x+y) both sides
z=-z
therefor z=0 since that is the only number that works

sub 0 for all z

we now have

x+y=4 and
3x+3y=12
that doesn't help

infinitely many solutions for x and y and z=0
the solution is the line x+y=4 or y=-x+4 and z=0 (since z=0, the graph is on the xy plane)

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