Average age of 5 students of a school is 14 years. The average age of students and their Mathematics and science teachers is 30 years. If the age of science teacher is 6 years more than the age of Mathematics teacher, then what is the age (in years) of Mathematics teacher?
A boat goes 15 km upstream and 10 1/2 km down stream in 3 hrs 15 min. It goes 12 km upstream and 14 km downstream in 3 hrs. What is the speed of the boat in still water?