How do you solve problems like these:
1. The difference between two-thirds of a number and one-sixth of the same number is 75. What is the number?
2. The numerator of a fraction is 4 less than its denominator. If the numerator and the denominator are decreased by 3 units, the fraction resulting is 5/6. What is the original fraction?
3. The tens digit of a two-digit number is one more than twice the units digit. Find the number if the sum of the digits is 13.
4. Arnel is 42 years old and his daughter Maris is 12 years old. In how many years will he be twice as old as his daughter?
5. Mrs. Reyes' age is 4 years more than 3 times her daughter's age. The sum of their ages is 44 years. Find the present ages of both.