your result is correct, despite your argumentation being wrong. you're starting from the premise that the price is 2$, probably because it's an option on the test. the actual premise is that you've got 1$ and the price (p) is 1$ + 0.5p. to satisfy both conditions, the price needs to be 2$. if it was 3$ + 0.5p, it would need to be 6$.
Catalonia