A merchant bought 300 apples at the rate of 5 for RS.90 and sold 120 of them at Rs.300 per dozen. If he wants to make a profit of RS.2100 in all, at what rate per dozen should he sell the rest of them?​

I think he should continue with the same rate of Rs300 per dozen to gain profit of Rs2100

At the rate of Rs 90 pre 5 apples he have to pay Rs 5400 for 300(25 dozen) apples.

total he have 25 dozen of apples.if he sold 12 dozen of appels at 300 per dozen then he earns Rs 3600. according to the merchant goal he wanted to make profit of 2100.we will add rs 2100 to CP hence we will get SP of Rs 5400+2100=7500. if he had already sell 12 dozens at rs 3600 then we will reduce the amount from SP hence we will get Rs 3900 to be earn. 13 dozens of apple is left so we can divide 3900/13 and we will get Rs 300.

if he continues selling those remaining 13 dozens of apple at the same rate the he can make profit of rs 2100.