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 ```Please include a comment with each solution indicating the amount of time spent solving it. Note: Using the two access functions of (units-digit) and (all-but-units-digit) and/or substitution or recursion functions. (decimal-length n) ; returns the number of digits in the number. EXAMPLE: (decimal-length 348567) --> 6 (ith-digit n i) ; returns digit which is the ith from the left. EXAMPLE: (ith-digit 471835629 4) --> 8 (leading-digit n) ; returns the first digit. EXAMPLE: (leading-digit 5394) --> 5 (occurance d n) ; returns the number of times digit d occurs in n. EXAMPLE: (occurance 6 549457654987587654655478563) --> 4 (digit-sum n) ; returns the sum of the digits in n. EXAMPLE: (digit-sum 2354) --> 14, (digit-sum 8) --> 8 (digital-root n) ; returns the result of repeatedly applying digit-sum until the result is a single digit. EXAMPLE: (digital-root 341943) --> (via 3+4+1+9+4+3=4, then 2+4=6) (backwards n) ; returns the digits in reverse order. You do not need to handle leading or trailing zeros. For this problem you may use multiplication. EXAMPLE: (backwards 329145) --> 541923```
 ```Dear kenobob, Here you go. (define (decimal-length n) ; 4 minutes (if (< n 10) 1 (+ 1 (decimal-length (all-but-units-digit n))))) (define (ith-digit n i) ; 3 minutes (if (= i (decimal-length n)) (units-digit n) (ith-digit (all-but-units-digit n) i))) (define (leading-digit n) ; 1 minute (ith-digit n 1)) (define (occurrence d n) ; 6 minutes (+ (if (= (units-digit n) d) 1 0) (if (< n 10) 0 (occurrence d (all-but-units-digit n))))) (define (digit-sum n) ; 2 minutes (+ (units-digit n) (if (< n 10) 0 (digit-sum (all-but-units-digit n))))) (define (digital-root n) ; 1 minute (let ((x (digit-sum n))) (if (< x 10) x (digital-root x)))) (define (backwards n) ; 8 minutes (letrec ((backward (lambda (n part) (if (= n 0) part (backward (all-but-units-digit n) (+ (* 10 part) (units-digit n))))))) (backward n 0))) If you don't already have definitions for units-digit and all-but-units-digit, you can insert the following before all the above definitions. (define (units-digit x) (modulo x 10)) (define (all-but-units-digit x) (/ (- x (units-digit x)) 10)) Regards, leapinglizard```