a)

(hop 2)
;=> 
(cond [(zero? 2) 1] [else (local [(define x (+ 2 2))] (* x (hop (sub1 2))))])
;=> 
(cond [false 1] [else (local [(define x (+ 2 2))] (* x (hop (sub1 2))))])
;=> 
(cond [else (local [(define x (+ 2 2))] (* x (hop (sub1 2))))])
;=> 
(local [(define x (+ 2 2))] (* x (hop (sub1 2))))
;=> 
(define x_47 (+ 2 2))
(* x_47 (hop (sub1 2)))
;=> 
(define x_47 4)
(* x_47 (hop (sub1 2)))
;=> 
(define x_47 4)
(* 4 (hop (sub1 2)))
;=> 
(* 4 (cond [(zero? 1) 1] [else (local [(define x (+ 1 1))] (* x (hop (sub1 1))))]))
;=>
(* 4 (cond [false 1] [else (local [(define x (+ 1 1))] (* x (hop (sub1 1))))]))
;=>
(* 4 (cond [else (local [(define x (+ 1 1))] (* x (hop (sub1 1))))]))
;=>
(* 4 (local [(define x (+ 1 1))] (* x (hop (sub1 1)))))
;=>
(define x_48 (+ 1 1))
(* 4 (* x_48 (hop (sub1 1))))
;=>
(define x_48 2)
(* 4 (* x_48 (hop (sub1 1))))
;=>
(define x_48 2)
(* 4 (* 2 (hop (sub1 1))))
;=>
(* 4 (* 2 (hop 0)))
;=>
(* 4 (* 2 (cond [(zero? 0) 1] [else (local [(define x (+ 0 0))] (* 0 (hop (sub1 0))))])))
;=>
(* 4 (* 2 (cond [true 1] [else (local [(define x (+ 0 0))] (* 0 (hop (sub1 0))))])))
;=>
(* 4 (* 2 1))
;=>
(* 4 2)
;=>
8


b)

(local [(define num-usd 500)] (us-to-can num-usd))
;=>
(define num-usd_23 500)
(us-to-can num-usd_23)
;=>
(define num-usd_23 500)
(us-to-can 500)
;=>
(* 500 conversion-rate)
;=>
(* 500 1.05)
;=>
(* 500 1.05)
;=>
525


c)

(local [(define conversion-rate 0.75)] (us-to-can num-usd))
;=>
(define conversion-rate_28 0.75)
(us-to-can num-usd)
;=>
(define conversion-rate_28 0.75)
(us-to-can 1000)
;=>
(define conversion-rate_28 0.75)
(* 1000 conversion-rate)
;=>
(define conversion-rate_28 0.75)
(* 1000 1.05)
;=>
;=>
(define conversion-rate_28 0.75)
(* 1000 1.05)
;=>
1050