For the following grouped data of monthly mobile-recharge amounts (in ₹), some frequencies are missing.
Class interval (₹): 0–10 10–20 20–30 30–40 40–50
Frequency: 6 12 xy 10
The total number of customers is 70 and the mode of the data is ₹25.33. Find the frequency x of the modal class.
(a) 32
(b) 28
(c) 24
(d) 30