Which chemical equation shows that the total mass during a chemical reaction stays the

The sum means to add two numbers so we can write : x + y = 18

Then, their difference is 4 which can be written : x - y = 4

The best way to determine this is to set one of the variables on one side of an equation to use in the second equation. This takes a bit of algebra.

x + y = 18 can be rearranged to x = 18 - y OR y = 18 - x : either of these gives you an equation to plug in to the second equation to find one of the variables.

x - y = 4 , from the equation we rearranged before, y = 18-x so we can plug this equation in for y

x - (18-x) = 4

Now we only have x to solve for :

x-18 +x = 4 (the second x becomes a plus because of the negative on the outside of the parenthesis.

then if we add18 on both sides:

x +x = 4 +18

simplify : 2x = 22

x = 11

Then we plug 11 into the previous equations we started with:

x + y = 18 > 11 + y =18 > y = 7

x - y = 4 > does 11-7 = 4? Yes! So we found out that x = 11 and y = 7

Step-by-step explanation: this should be right