Trigonometry question. WILL GIVE LOTS OF POINTS

If 20% of a number is 35, what is 50% of that number?

How do you use the elimination method for this question? explain, because i really want to understand!

The bottom of ignacio's desktop is 74.5cm from the floor. ignacios sits in his adjustable chair, and the tops of his legs are 49.3cm from the floor. each clockwise rotation of the knob on the chair raises ignacio's legs by 4.8cm. write an inequality to determine the number of clockwise rotations, r, ignacio could make with the knob without his legs touching the desk.