Step 1 :Let's denote the number of customers who wanted mustard as \(m\) and the number of customers who did not want mustard as \(n\).
Step 2 :Given, \(m = 36\) and \(n = 78\).
Step 3 :Total number of customers is the sum of mustard and non-mustard customers: \(t = m + n\).
Step 4 :Calculate the total number of customers: \(t = 36 + 78 = 114\).
Step 5 :The experimental probability of the next customer wanting mustard is the ratio of mustard customers to the total customers: \(P(\text{mustard}) = \frac{m}{t}\).
Step 6 :Calculate the probability: \(P(\text{mustard}) = \frac{36}{114} = \frac{18}{57}\).
Step 7 :\(\boxed{P(\text{mustard}) = \frac{18}{57}}\)