By selling $80$ ball pens for $₹ 140$,a retailer loses $30 \%$. How many ball pens should he sell for $₹ 104$ so as to make a profit of $30 \% ?$

$A$ shopkeeper allows a discount of $12.5 \%$ on the marked price of a certain article and makes a profit of $20 \%$. If the article costs the shopkeeper $Rs. 210$,then the marked price of the article will be (in $Rs.$)

$A$ cloth merchant says that due to a slump in the market,he sells cloth at a $10 \%$ loss,but he uses an inaccurate metre scale and actually gains $15 \%$. Find out the actual length of the scale (in $cm$).

$A$ man purchased $150$ pens at the rate of $Rs. 12$ per pen. He sold $50$ pens at a gain of $10 \%$. The percentage gain at which he must sell the remaining pens so as to gain $15 \%$ on the whole outlay is........$\%$

$A$ sells a bicycle to $B$ at a profit of $20 \%$ and $B$ sells it to $C$ at a profit of $25 \%$. If $C$ pays $Rs. 1500$,what did $A$ pay for it in $Rs.$?

$A$ dealer fixed the price of an article $40 \%$ above the cost of production. While selling it,he allows a discount of $20 \%$ and makes a profit of $Rs. 48$. The cost of production (in $Rs.$) of the article is: