Theo's mom bought an 8 pack of juice boxes at the store for $4. find the unit rate for the juice boxes

The unit rate for the juice boxes is approximately 0.5

Question 1:
It's mostly a preference problem. You can do any of those options and still be correct. The easiest is to solve for y in the second equation. All you have to do is subtract 2x.

Question 2:
x is already solved for. graphing doesn't matter in the substitution method. Since x is already solved for, then it would be easy to substitute 2-y for x in the second equation.

Question 3:
If you are given x, then just substitute the value for x in the y = equation.
x = 10
y = 3x - 5

y = 3(10) - 5
y = 30 - 5
y = 25