For the answer for part b, why's x>0??

Someone answer this asap for gabriella uses the current exchange rate to write the function, h(x), where x is the number of u.s. dollars and h(x) is the number of euros, the european union currency. she checks the rate and finds that h(100) = 7.5. which statement best describes what h(100) = 75 signifies? a. gabriella averages 7.5 u.s. dollars for every 100 euros. b. gabriella averages 100 u.s. dollars for every 25 euros. c. gabriella can exchange 75 u.s. dollars for 100 euros. d. gabriella can exchange 100 u.s. dollars for 75 euros.