write an equation to solve each problem

There is only one freshman in the cast of the high school musical. There are 6 sophomore and 11 juniors. One third of the cast are seniors. How may seniors are in the musical?
*Please show me the work on how to do it

1 answer

1+6+11 = 18 = 2/3 of cast
so
cast = 27
27 - 18 = 9
which is indeed 1/3 of the cast