spent : voucher = 15 : 2

nos.
bottles: 3
bars: 2

unit cost
bottle: 3u
bar: 4u [ 4u = 2/3 x 2 x 3u ]

cost
bottles: 3u x 3 = 9u
bars: 4u x 2 = 8u


$8 worth means spent 15x4 = $60

actual $ spent = 60-6.45 = $53.55


9u + 8u = 53.55
1u = 3.15


1 bar costs $12.60

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Hi Snell, I still don’t understand how 1 bar is 4u. Can you explain? Thank you.

sure, no prob

In the qn, it states that:
"Each bar of soap costs 2/3 as much as 2 bottles of shampoo."

this means
cost of 1 bar = 2/3 x 2 bottles

since i set cost of 1 bottle to 3units,
2 bottles would cost 2 x 3 = 6u
&
the cost of 1 bar in units would be:
2/3 x 6u = 4u

[ in case u ask why 3units, it is due to the fraction '2/3'.
juz wanna make it a nice no. to work with.
u can set it at 6u or 9u or any multiples of 3.
OR if u wanna confuse urself a bit, u can set it 1unit or 4units or any no. u like. ]

Ok I understand now. Thanks very much for your detailed explanation!