Answer
The point of intersection is (4,48) which means that an order of 4 tickets will have the same total cost when ordering online or at the door.
Work Step by Step
$(a)$
Ordering online, the cost is 10dollar $\times$ t $+$ 8dollar a service charge.
The equation for online order is
$c = 10t + 8$
Buying at the door will cost 12dollar $\times$ t
The equation for Buying at the door is
$c= 12t$
The System of equation is
$c = 10t + 8$
$c = 12t$
$(b)$
The Graph will be$:$
