For each of the following recurrences, sketch its recursion tree, and guess a good asymptotic upper bound on its solution. Then use the substitution method to verify your answer. a. T(n)=T(n/2)+n3. b. T(n)=4T(n/3)+n. c. T(n)=4T(n/2)+n. d. T(n)=3T(n1)+1