請益對數有關的問題 - 經濟

Suppose the monthly demand for coffee is estimated as

ln(Q) = 7.5 - .1 ln(P) + .3 ln(I)

where Q is the quantity, P is the price, I is community income, and ln
denotes the natural logarithm. If price rises by 20 percent and income rises
by 10 percent, the quantity of coffee demanded will fall.

a. The above statement is true.
b. The above statement is false.
c. The above statement may be true or false.

原先第一次寫的時候沒有注意到logarithm這個字所以帶了兩組數字進去得到答案c XD
但是答案是B (表示Q應該要上升才對?) 請問這種含有ln的式子該怎麼看或者快速判讀?

感謝


--