The cost price of $6$ pens is equal to the selling price of $4$ pens. Find the profit percent. (in $\%$)

$A$ man sells two articles for $Rs. 5000$ each,neither losing nor gaining in the deal. If he sold one of them at a gain of $25 \%$,the other article is sold at a loss of .......$\%$

$A$ trader buys two articles for $Rs. 4000$ each. While selling,if he gains $12.5\%$ on one and loses $20\%$ on the other,what will be the overall loss percent (in $\%$)?

$A$ shopkeeper sells sugar in such a way that the selling price of $950 \ g$ of sugar is the same as the cost price of $1 \ kg$ of sugar. What is his gain percent?

Rita buys an article for $Rs. 9600$. She sold it at $12\%$ loss and gets some money,and from that money,she again buys an article and this time she gets $12\%$ profit. What was the profit or loss she got from this transaction in $Rs.$?

$A$ sells an article to $B$ at a gain of $20 \%$,$B$ sells it to $C$ at a gain of $10 \%$,and $C$ sells it to $D$ at a gain of $12 \frac{1}{2} \%$. If $D$ pays $Rs. 29.70$,what was the cost price for $A$? (in $Rs.$)