math
posted by thomas .
HHow many pupils are there in a class if two pupils remain after four rows of seats are filled, and nine pupils remain after three rows of seats are filled?
a. 21
b. 22
c. 28
d. 30
e. 32
please answer and explain

If there are 9 left over from 3 rows and 2 left over from 4 rows, each row must seat 92 = 7 pupils
So, 7*4 +2 = ?
Or, 7*3 +9 = ?