X= adult tickets
Y= Children tickets
You need two equations one is number of people
Second formula is the money
X+y= 429
1x+ .75Y= 372.50
You can use the substitution or elimination method
I will use substitution make X = 429-y using the 1st equation then put it in the 2nd
429-1y+.75y= 372.50
429 -.25y= 372.50
-429. -429
-.25y=. -56.5
Divide both side by -.25
y= 226
So 429-226= 203 for X
203 adult tickets and 226 children tickets