Can someone me with these 2 last homework questions

31a) Think of $30.90 as 100% of her bill, we first want to find 6%
To work out how much this is, we need to divide the percentage by 100 to get a multiplier (decimal)
6/100 = 0.06
Multiply 0.06 and $30.90 to get the tax
$30.90 x 0.06 = 1.854
As we can't have part of a cent, we round to the nearest 100th
If the number to the right of this value is below 5 we round down, 5 or more we round up
4 is below 5 so we round down
$1.85

31b) For the total bill, we need to add together the original and the tax
$30.90 + $1.85 = $32.75

32a) Simple Interest = PRT
This means
P x R x T
We need to multiply together the Principal, Rate and Time span
We need to turn the percentage into a decimal, so we divide by 100 like before
3.2 / 100 = 0.032
$750 x 0.032 x 6 = $144

32b) To find the account balance, we need to add the interest to the original amount
$750 + $144 = $894