懂英文和数学的来!百分数问题.There are 75 passengers in a double-decker,an

懂英文和数学的来!百分数问题.
There are 75 passengers in a double-decker,and 40% of them are on the upper deck.
(a)How many passengers are there on the lower deck?
(b)If 30% of the passengers on the upper deck are children,how many chidren are there on the upper deck?