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X = 14,400 / 0.2 = 總售價
X = $72,000.00 (故總售價為$72,000.00)

零售價為 總售價 除以 賣出份數
所以: 72000 / 4800 = $15.00

因為已知獲利為20%﹐ 故每份套餐獲利亦一樣為20%
15.00 x 20% = $3.00

答: 每份套餐的成本 = 12.00
每份套餐售價 = 15.00

The calculation is wrong.
$72,000 is the toal cost not the total sale;

Thus each set cost $15 with 20% gain ($3) giving the selling price is $18.

每份獲利= 14400 / 4800 = 144/ 48 = 3


3 = (20%)成本

x 5 both side ( 20 % = 0.2 and 0.2 x 5 = 1)

成本= 15

售價= 15+3 = 18

成本:15 元
售價:18 元

設 每份成本 是 C 元
設 每份售價是 S 元

4800 x ( S -C ) =14400
S-C =3
S = C +3

(S -C ) / C = 20%
( C +3 -C )/ C =0.2
3/C =0.2
C = 3/0.2
C =15 //

S = C+3
=18 //
每份成本是 15 元, 售價是 18 元