if 3 times a less than a number n is the same as the number

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