well, is very straightforward, she's got the 6 toffees for $1, now to get a gain of 20%, let's just up the $1 to 20%, well, very straight one buck plus 20% is just one buck and 20 cents, or $1.2. What the heck all that means?
well, it means that she must sell all 6 tofees for $1.20, we can just divide hmmm 1.2 ÷ 6 = 0.2, meaning, she must sell each at 20 cents, so if she sells 5 of them at 20 cents, that'd be one rupee, what she paid for all, the last toffee will be the extra or the gain of 20%.