We know we have 30 rows in the pavillion. We know we have 20 seats in the first row, and that we add 6 seats to every subsequent row.
Now if we have 30 x 20, then that is the starting numer of seats at 600 and we add 6 seats to each of the remaining 29 rows so we could multiply 29 times 6 for a total of 174 and add that to the original for a total of 774.
However I have a sneaking suspicion I have over simplified by adding jut 6 seats to each row rather than a progressive number where there are 6 added to the second row and then 12 to the thitrd ro and so on and so on. I am not certain how to calculte that progression into this equation but I suspect it relies upon an exponent for that calculation so I am off to see if I can find it....
I think you have to find a common multiple for the denominators 5 and 8 which would be 40. so it would be 6/40 and 2/40. then I think, you would add or multiple, depending on the situation, 6 and 2
