There are two ways to do this.
You can either add 5% of 800 (use cross-multiplication to do this) to 800, then multiply by 23, or multiply 800 by 23, then add 5% of that to the answer.
Method 1:
*(5/100) x (x/800)
*5 x 800 / 100 = 40
*800 + 40
*840 x 23 = 19320
Method 2:
*800 x 23
*18400
*(5/100) x (x/18400)
*5 x 18400 / 100 = 920
Answer = 920
