It is important to do the same thing to both sides of an equation because in the end, both sides will be equivalent, or equal, therefor making the problem true. If you didn't do the same thing on both sides of an equation, one side would be incorrect and not equal to the other side. Hope this helps! Please mark brainliest. Thank you v much! :)
Top one would be 18 on the pyramid.
Using substitution:
first you have to express one variable in terms of the other, in this we can express y in terms of x:

Since both expressions are equal to y, you have to equal both expressions like this:

Now you can solve the equation:

Knowing x=10, you can use any of the expressions we found before to find y. In this case I'm going to use y= -x+9 because it's simpler but boy should give you the same result

So, the answer is x=10 and y=-1
Answer:

Step-by-step explanation:
