Question 1137276

the first row:  {{{a[1]=16}}}
 the second row: {{{a[2]=18=16+2}}}
 the 3rd row: {{{a[3]=20=18+2=16+4}}}
so on through row {{{60}}}

{{{a[n] = a[1] + d * (n - 1)}}}

row {{{60}}} will have

{{{a[60] = 16 + 2 * (60 - 1)}}}
{{{a[60] = 16 + 2 * 59}}}
{{{a[60] = 134}}}

the total number of seats in the first row through row {{{60}}} is:
the sum of an arithmetic sequence is: 

{{{S[n] = n * (a[1] + a[n]) / 2}}}

{{{S[60] = 60* (16 + 134) / 2}}}

{{{S[60] = 30* 150}}}
{{{S[60] = 4500}}}

if row through {{{60}}} to {{{80}}} has the same number of seats, we have
{{{20*134=2680}}}

 the total number of seats in the auditorium is {{{4500+2680=7180 }}}