Method 1:
Cost of one third of land=150000/3 = 50000 Rs
At 6% loss sale price=50000*94/100 =47000 Rs
To get 10% profit the final sale price =150000*110/100=165000 Rs
He has to sale 2/3 of land at 165000 - 47000 =118000 rs
Purchase price of 2/3 land =150000*2/3 = 100000
The gain % = (118000-100000)*100/100000=18%
He has to sale remaining land at 18% profit.
Method 2:
10% of Rs. 150000= Rs. 15000
So, total selling price = 150000+15000=Rs.1,65,000
Cost price of 1/3rd of of the land is 1,50,000/3=50,000.
6% of 50,000=Rs. 3000
Selling price of1/3rd of land = 50000-3000=Rs. 47000
The cost price of remaining piece of land = 1,50,000-50000=1,00,000
Selling price of ramaining land must be =1,65,000-47000=118000
Gain = 118000-100000=Rs. 18000
Gain %= gain/cost price * 100 = 18000/100000 * 100=18%