Clue box:

1 Magnet = 1u+10 –> 12 magnet = 12u+120 (used 3/5 money) = 9/15

1 Keychain = 1u    –> 8 keychains = 8u (used 5/6 of remainder = 5/6 x 2/5 = 1/3 money) = 5/15

Diff is 9/15 – 5/15  = 4/15 –> 4u+120

[Then by analysing fractions… I think I got lucky to have easily divisible units and constants…]

                                      1/15 –> 1u+30

                                      5/15 –> 5u+150   —> =8u above –> u=50

(or                                9/15 –> 9u+270   —> =12u+120 above –> u=50)

Total at first = 15u+450 = 1200 cents = $12#

(checked – 1 Keychain is 50 cents and 1 Magnet is 60 cents)

key chain ——- 1u
magnet ——- 1u + 10
5 x 6 = 30
Henry’s money at first ——- 30p
(3/5) x 30p = 18p ——- 12 x (1u + 10) = 12u + 120
6p ——- 4u + 40
30 – 18 = 12
(5/6) x 12p = 10p ——- 8 x 1u = 8u
5p ——- 4u
6p – 5p = 1p ——- 40
30p ——- 30 x 40 = 1200
1200 cents = $12

Ans : $12.