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 $30 \%$?

Sarita sells a phone at a profit of $20 \%$. If she had bought it at $20 \%$ less and sold it for $Rs. 180$ less, she would have gained $25 \%$. Find the cost price of the phone in $Rs.$

$A$ man buys $10$ articles for $Rs. 8$ and sells them at $Rs. 1.25$ per article. His gain percent 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 $Rs.$?

$A$ shopkeeper mixes $26 \, kg$ of wheat which costs $Rs. 20$ per $kg$ with $30 \, kg$ of wheat which costs $Rs. 36$ per $kg$ and sells the mixture at $Rs. 30$ per $kg$. Find the profit percent. (in $\%$)

$A$ man sells a scooter to his friend at $10\%$ loss. If the friend sells it for $₹ 54000$ and gains $20\%$,find out the original cost price of the scooter. (in $₹$)