There are 21 supervisors in total
Solution:
Given that, To get to zoo from the school the kids have to ride some buses
There are 7 buses and each bus have three adult supervisors to guard the children
To find: Number of supervisors in total
From given,
Total number of buses = 7
Number of supervisor in 1 bus = 3
Therefore, total number of supervisors can be found by multiplying total number of buses with number of supervisors in 1 bus

Substituting the values we get,

Thus there are 21 supervisors in total