The formula to solve the volume of a 3-D shape is length times width times height. So you would multiply 8 times 6 times 4. Then you just add the descriptions.
Deborah has to pay 9% for tax. So is someone worked on her computer for two hours then she pays 9% on $120 worth of work. So her tax amount would be $10.800 and her total amount would be 10.8 +120 = $130.80.