At the city museum, child admission is $5.70 and adult admission is $9.20. On Wednesday, 151 tickets were sold for a total sales of $1074.20. How many adult tickets were sold that day?

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