X^2+8=10x complete the square

How do you do this geometry problem

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

Bill works as a waiter and is keeping track of the tips he ears daily. about how much does bill have to earn in tips on sunday if he wants to average $22 a day? tips by day tips (dollars) monday tuesday wednesday thursday friday saturday $14 $22 $28 $36