To qualify in a competition, Sukanya needs an average score of 105 across four examinations. Her scores in the first three exams are 137, 107, and 77. How many marks must she score in the fourth exam to qualify?

The average of 100 numbers is 40. If one of the numbers, 30, is replaced by 70 while keeping the other numbers same, what is the new average?

The arithmetic mean of 22.5, 56, 42.5, 2x + 1, x - 2, 3x, and 36 is 30. Find the value of x (where x > 0).