Let's define the variable:
Let \( x \) be the original cost of each admission ticket.
Since there are 4 people (you and 3 friends), the total cost for all admission tickets can be expressed as:
\[ 4x \]
According to the problem, the total cost to get into the carnival before using the coupon is $100. With the $20 coupon, the total cost becomes:
\[ 4x - 20 = 100 \]
To find the original cost of each admission ticket, we first add $20 to both sides of the equation:
\[ 4x = 100 + 20 \] \[ 4x = 120 \]
Next, we divide both sides by 4 to find \( x \):
\[ x = \frac{120}{4} \] \[ x = 30 \]
Therefore, the original cost for each admission ticket is $30.
In complete sentence: The original cost for each admission ticket to the town carnival is $30.