Using quick mental math, we can do 8% of 10 to get 0.8, which is close to the value of 0.0845*10. Also fairly quick is moving the decimal point over 1 spot to the right and we go from 0.0845 to 0.845 and that rounds to 0.8 when rounding to one decimal place. Recall that 8.45% = (8.45/100) = 0.0845
If you want to compute out the four results with a calculator, then it would look like this: 0.0845*20 = 1.69 0.0845*25 = 2.1125 0.0845*10 = 0.845 0.0845*18 = 1.521 and this shows that no other result (but choice C) is close to 0.8
