so remember that you can do anything to an equation as long as you do it to both sides so
try to get all the placehlders on one side
2z-31=-9z+24
we decide to bring allthe placeholders (z) to the left since that has more z's and move the other numbers to the right
2z-31=-9z+24
add 9z to both sides
11z-31=24
add 31 to both sides
11z=55
divide both sides by 11
z=5
answer is z=5