Answer:
Adults pay $20 while children pay $17
Step-by-step explanation:
Let price for adults be x while children be y
First case
Three adults and four children must pay $128
3x+4y=128
Second case
Two adults and three children must pay $91
2x+3y=91
To make x the subject
2x=91-3y
X=45.5-1.5y
Solving equations
By substituting x with 45.5-1.5y into
3x+4y=128
3(45.5-1.5y)+4y=128
136.5-4.5y+4y=128
0.5y=8.5
Y=2*8.5=17
X=45.5-(1.5*17)=20
Therefore, adults pay $20 while children pay $17