standard_description: Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.
problem_activity: Problem 1
Solve the system of linear equations using substitution. Describe how you can solve any system using substitution.
$${x+2y=8}$$
$${-3x+2y=16}$$
Problem 2
Solve the two systems below using substitution. Compare and contrast the two solutions. What do they each mean?
|          **           System A          **          |          **           System B          **          |
|-----------------------------------------------------|-----------------------------------------------------|
| $${y=2(-x+3)}$$                        $${2x+y=4}$$ | $${5x+20y=15}$$                        $${x+4y=3}$$ |


aligns: no