10% as a decimal (a value between 0 and 1) is 0.1
The only rule to follow is
Divide dividend by divisor and the mention the quotient and things left after remains in place of remainder
Here is a sample

Answer: $11.60
Explanation: First, you want to do 15.1 - 9.3 to find what half of his weekly allowance is, and that would be 5.8, AKA $5.80. Next, you want to multiply that number by 2, which would be 5.8(2) to get 11.6, or your final answer, $11.60.