4. Queue is a linear data structure that implements First-In First-Out (FIFO). It can be implemented using array and also singly-linked list. Suppose Figure 2 shows a queue that is implemented using circular array with front index at 3 and rear (or back) index at 1. a. [2 marks] Draw the singly linked-list illustrating the original queue in Figure 2. b. [1 mark] Determine the size (number of items) in the queue in Figure 2 . c. [1 mark] Determine the front index and rear index if enqueue (21) is performed on the queue in Figure 2. d. [1 mark] Using circular array, when rear index = front index 1 , the queue is considered full. The same situation is also observed when the queue is empty. Explain how to distinguish between these two situations (queue is full and empty)