$A$ dishonest dealer professes to sell his goods at cost price but uses a weight of $960 \, g$ instead of a $1 \, kg$ weight. Find his gain $\%$. (in $\%$)

On selling an article for $Rs. 170$,a shopkeeper loses $15\%$. In order to gain $20\%$,he must sell that article at rupees:

$A$ man buys an article for $Rs. 27.50$ and sells it for $Rs. 28.60$. Find the gain percent. (in $\%$)

When a producer allows $36 \%$ concession on the retail price of his product,he earns a profit of $8.8 \% .$ What would be his profit percent if the concession is reduced by $24 \% ?$

In these questions,two equations numbered $I$ and $II$ are given. You have to solve both the equations and mark the appropriate option.
$I.$ $2x^2 + 19x + 45 = 0$
$II.$ $2y^2 + 11y + 12 = 0$

$A$ white goods dealer pays $10 \%$ custom duty on an iPhone that costs $Rs. 25000$ in $UK$. For how much should he mark it,if he desires to make a profit of $20 \%$ after giving a discount of $25 \%$ to the buyer? (in $Rs$)