It’s the first answer - ie the equation needs to be balanced.
You can’t just look at the individual elements. To balance the equation, Magnesium will be part of the balancing and hence you will be adding Magnesium to both sides of the equation etc
We simply use the formula,

Given, velocity = 4 m per s and distance = 120 m.
Substituting these values, we get
.
Thus, required time for the elevator in order to travel 120 m upwards is 30 s.
Answer:
If iron, nickle, or cobalt is an answer choice, those are the three metals that are purely magnetic.