May I know the answer

Two times a number plus three times another number equals 4. three times the first number plus four times the other number is 7. find the numbers

You give a $4 tip for a meal that cost $22. approximately what percent of the bill was your tip?

What is the greatest number of parts of a circle that can be formed by cutting the circle with 7 straight cuts? (note: the parts do not have to be equal in size)