盈利既問題...唔該幫幫手...thx

以$1840出售一隻手錶，可獲利15% :

成本 x (1 + 15%) = 1840

成本 = 1840 / 1.15 = $1600

若要把盈利增加1倍,即要獲利 15% x 2 = 30% :

手錶的售價 = 成本 x (1 + 30%)

= 1600 x (1 + 30%) = $2080

let x be the original price of watch,
x(1+15%)=1840
x=1600

the benefits = 1840-1600
= 240

if we double the benefits = 240*2 + 1600
= 2080