3. Consider the following statement: In data structures, all trees are graphs. State the correctness of the above statement. Making use of suitable diagram(s), justify your answer. (10 marks) 4. Consider the following Java code for performing a computation on the required contents of an integer array, where first and last correspond to valid indexes in the integer array: public int compute (int [] array, int first, int last) { int result = 0; if (first < last) { result = array [first] + compute (array, first+2, last); else if (first < array.length) { result = array [first]; } return result; Making use of a suitable Big-O expression, state and explain in some detail the time complexity of method compute. Your explanation must include a justification for the chosen Big-0 expression and make reference to the number of calls to compute at Line 6. (8 marks)