GIVEN: James purchased Medicine A for x dollars, which included a sales tax of 5%
Let C = the cost of the medicine BEFORE TAX
So, 0.05C = the 5% sales tax James paid on the medicine
We can write: C + 0.05C = x
Simplify to get: 1.05C = x
So, C = x/1.05

In other words x/1.05 = the cost of the medicine BEFORE TAX
So, the sales tax James paid = 5% of x/1.05
= 0.05x/1.05

GIVEN: Kate was charged 5% for sales tax on x dollars that Medicine B costs
So, 0.05x = the 5% sales tax Kate paid on the medicine

We get:
QUANTITY A:0.05x/1.05
QUANTITY B:0.05x

At this point, we might already recognize that Quantity B is greater.
However to clear up any doubt, we can divide both quantities by 0.05x to get:
QUANTITY A:1/1.05
QUANTITY B:1

At this point, we can certainly see that Quantity B is greater

Answer: B

Cheers,
Brent

My answer as well