First, add all products she purchased to find out out total price she had to pay before taxes will be apply. That is: $3.50+$2.25+$9.95=$15.7
Now, 5% of this amount will be added dues to taxes, which is 5% of $15.7
5% of 15.7 = 5%•15.7= 5/100•(15.7)=78.5/100=0.785. This is amount will be added due to tax
Putting all together she has to pay $15.7 plus taxes $0.785 which is $16.485