Let N be the positive integer 7777…777, a 313-digit number where each digit is a 7. Let f(r) be the leading digit of the rth root of N. What isf(2)+f(3)+f(4)+f(5)+f(6)?(<spanclass=′latex−bold′>A</span>)8(<spanclass=′latex−bold′>B</span>)9(<spanclass=′latex−bold′>C</span>)11(<spanclass=′latex−bold′>D</span>)22(<spanclass=′latex−bold′>E</span>)29