To find the cost of an adult ticket, we need to solve the system of equations derived from the data provided. The equations we have are:
- \( 10a + 25c = 670 \) (from Friday)
- \( 5a + 10c = 290 \) (from Sunday)
Let's first simplify the second equation by dividing all terms by 5:
\[
a + 2c = 58
\]
Now we can express \( a \) in terms of \( c \):
\[
a = 58 - 2c
\]
Next, we can substitute this expression for \( a \) into the first equation:
\[
10(58 - 2c) + 25c = 670
\]
Expanding this gives:
\[
580 - 20c + 25c = 670
\]
Combining like terms:
\[
580 + 5c = 670
\]
Now, subtract 580 from both sides:
\[
5c = 90
\]
Dividing by 5 gives:
\[
c = 18
\]
Now that we have the cost of a child ticket, we can substitute \( c = 18 \) back into the equation for \( a \):
\[
a = 58 - 2(18)
\]
\[
a = 58 - 36
\]
\[
a = 22
\]
Thus, the cost of an adult ticket is $22.