How is this equation wrong?? I’m giving brainlest

It isn't?

Step-by-step explanation:

Step 1:

x + 8y = 21

x + 8y - 8y = 21 - 8y

x = -8y + 21

Step 2:

(-8y + 21) + 8y = 21

-8y + 21 + 8y = 21

21 = 21

a) one student is chosen from classroom a, then a student is chosen from classroom b.  

step-by-step explanation:

independent events are ones in which the probability of one event does not affect the probability of the second event.

one student is chosen from classroom a; this does not affect the chances of choosing a student from classroom b.   this makes these independent events.

when one card is chosen from a standard deck and then set aside before a second card is chosen, the probability of the second card being chosen changes.   this makes them dependent events.

when one student is chosen from classroom a and then a second student is chosen from classroom a, the probability of choosing the second student changes.   this makes them dependent events.

when a letter is chosen from the alphabet and then a second letter is chosen, the probability of choosing the second letter changes.   this makes them dependent events.