c= child tickets
a = adult tickets
c+a = tickets sold
c+a = 151
solve for c
c= 151-a
child tickets * child ticket price + adult tickets sold * adult ticket price = total sales
c*5.70 + 9.20*a = 1074.20
substitute for c
(151-a) * 5.70 + 9.20 *a = 1074.20
distribute
860.7 - 5.7a + 9.20a = 1074.2
combine like terms
860.7 +3.5a = 1074.2
subtract 860.7 from each side
3.5a = 1074.2 - 860.7
3.5a = 213.5
divide each side by 3.5
a = 213.5/3.5
a =61
There were 61 adult tickets sold