The first probability problem is quite easy since the numbers are percentages.
Quick refresher: 1% is 1/100
Since 45% of customers want their plate sets to be moved, you would think its 45/100, but actually you also need to add the people that need both of their sets moved, which includes plate sets. It would be 50/100 ( ill let you simplify)
Second question
Since the knife sets have been moved, a 25% probability, we know that 50% of customers want their plates moved. However, it is no longer 50/100 but 50/75 (simplify). This is because there are only 75% of customers remaining.
I may have made a mistake, but hopefully this makes it clearer. :)