Hey there!! 
Let's take a closer look at the question, 
We have the original price with included 15% tax 
This original price is first reduced by 35% , first let's solve this. 
35% = 35 / 100 = 0.35 
0.35 × 1899 
... $664.65 = 35% of of $1899.00 
It would be sold for 
... 1899 - 664.65 
... $1234.35
Now, this price is further reduced by 20% 
20% = 20/100 = 0.20 
... 0.20 × 1234.35 
... $246.87 
This is 20% of 1234.35 
Now, the price it would be sold for = 
... $1234.35 - $246.87 
... $987.42 is the final price the sofa would be sold for. 
Hope my answer helps!!