Emily had 75 buttons. She gave 15 to Jake. What percent of buttons did she give to Jake?

Solve: 3x+y=6 4x-2y=18 show all work !

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

The? half-life of a radioactive substance is 20 years. if you start with some amount of this? substance, what fraction will remain in 120 ? years