At the city museum, child admission is $5.20 and adult admission is $9.10. on saturday, three times as many adult tickets as child tickets were sold, for a total sales of $975.00. how many child tickets were sold that day?

30 child tickets were sold that day.

adult tickets = a
child tickets = c

9.1a + 5.2c = 975
a = 3c

Substitute a into the first equation
9.1(3c) + 5.2c = 975
Simplify
27.3c + 5.2c = 975
Combine like terms by adding
32.5c = 975
Divide both sides by 32.5 to isolate the variable c
c = 30