Question 11292
Let the age of the gym = G
then Age of auditorium=G+21
Also Gym = (1/4)Auditorium
    G= (1/4)(G+21)
Multiplying both sides with 4
4G=G+21
Subtracting G on both sides
3G=21
G=7
Therefore Auditorium = 21+7 = 28