if 3 times a less than a number n is the same as the number number increased by a4 ,what is n

题目

if 3 times a less than a number n is the same as the number number increased by a4 ,what is n
a motor boat traveling at 18 miles per hour traveled the length of a lake in one quater of an hour less time it took when traveling at 12 miles per hour ,what was the length in miles of the lake
George spent 25% of the money he had on lunch and 60% of the remaining money on dinner .if he then had 9.00yuan left how much did he spend on lunch

答案

（1）n的1/3跟n+4一样大,求n?
（2）一条摩托艇以18英里每小时穿过这个湖比用12英里每小时穿过少用时15分钟,问这个湖有多长
（3）乔治花25%的钱吃午饭,60%的钱存着吃晚饭,当他吃完午饭后他还有9块钱,问他花了多少钱吃午饭?
应该都会做吧