(d) Merge sort is a well-known divide-and-conquer approach based on recursively splitting an input array into two sub-arrays of roughly half the size (divide stage) and then merging the sorted sub-arrays to sort the original input (conquer stage). Consider a variant of the merge sort algorithm which proceeds by recursively splitting the array into three sub-arrays of roughly a third of the size during the divide stage and then merging the sorted sub-arrays to sort the original input array during the conquer stage. Explain why the recurrence relation characterising the computational complexity T(N) of this variant of the algorithm is of the form: T(N) = 3 T(N/3) +cN, where c is a constant. [10%)