How do you simplify 2xy+3ab-4xy-9ab. show how you did it

2xy+3ab-4xy-9ab
2xy-4xy   3ab-9ab
-2xy              -6ab
        
answer = -2xy-6ab

2xy+3ab-4xy-9ab
First you wanna find like terms 
Like 2xy and -4xy they have the same letters
SO do 2xy-4xy and you should a negative number like -2xy make sure after you subtract you and the letters one the number
Now do 3ab and -9ab the same way i did it with the other like terms you subtract and should get -6ab so after you gotten both of thoss solved you should have the expression
    -2xy-6ab
Hope this helped :)

Aand b are correctly balanced reactions. they have the same number of atoms in both sides of the reaction

The answer would be 27 because assuming that each package has 1 bar of soap and 1 tube of toothpaste, after 27 packages they would run out of toothpaste