The whole bill is $31.99 that is 100%. You can use mental math to determine exatcly 15% from $31.99:
1. 15%=10%+5%
2. To find 10% from $31.99 you should simply divide $31.99 by ten. Thus, 10% from $31.99 is $3.199.
3. 5% is half of 10%, then 5% from $31.99 is $3.199:2=$1.5995.
4. 15% from $31.99 is $3.199+$1.5995=$4.7985≈$4.80.
Answer: correct choice is B.
