Find the difference per row:
10 seats in the first row
30 seats in the sixth row:
30 -10 = 20 seats difference.
6-1 = 5 rows difference.
20 seats / 5 rows = 4 seats per row.
This means for every additional row, there are 4 more seats per row.
The equation would be:
Sn = S +(n-1)*d
Where d is the difference = 4
S = number of seats from starting row = 10
n = the number of rows wanted
S(11) = 10 + (11-1)*4
S(11) = 10 + 10*4
S(11) = 10 + 40
S(11) = 50
Check:
Row 6 = 30 seats
Row 7 = 30 + 4 = 34 seats
Row 8 = 34 + 4 = 38 seats
Row 9 = 38 + 4 = 42 seats
Row 10 = 42 + 4 = 46 seats
Row 11 = 46 + 4 = 50 seats.
